Definitions beginning with D

Dark pattern

Interface choice designed to push users toward a decision they would not have made freely or clearly.

In practice: review sensitive choices so declining or going back is as understandable as accepting.

Data center

Physical facility housing servers, storage, networks, power and cooling systems.

In practice: Ask where data resides, who operates the facility and how continuity is provided.

Data export

Extraction of content or data into a reusable format; it does not necessarily include code and settings needed for a full restoration.

In practice: inspect a test export for media, relationships, URLs and metadata before treating it as an exit path.

Data minimization

Principle limiting personal data processed to what is relevant and necessary for a defined purpose.

Reference: CNIL · Minimisation · Source consulted 2026-10-31

In practice: justify each collected field by a concrete task and retention need.

Data table

Values organised in rows and columns with explicit headers. Preserve associations between cells and headings, and identify missing values and units to prevent misleading readings.

Reference: W3C WAI : Tables · Source consulted 2026-10-18

In practice: check row and column headers with keyboard and assisted reading.

data-nosnippet

HTML attribute supported by Google to exclude a visible portion of a page from certain search-result snippets.

In practice: Apply this attribute to a precise passage and inspect the rendered page after release.

Database

Organized collection of data generally queried and changed through a management system. A relational database uses tables and relationships, but not every database follows that model. An application’s media files and settings may be stored separately.

Reference: MySQL Reference Manual : Databases and relational data · Source consulted 2026-10-18

In practice: identify stored data, dependencies and required access before migration. Test a complete restoration: recovering table rows is insufficient if necessary files, links or relationships are missing.

DDoS

Denial-of-service attack using many hosts to disrupt a service’s availability.

Reference: NIST CSRC · Distributed denial of service · Source consulted 2026-10-31

In practice: Document who can act on traffic and how to keep an information page available during an incident.

Dedicated server

Physical machine reserved for one client or project, providing greater control and isolated resources.

In practice: Compare measured load and operating responsibility before choosing this option.

Deep link

Link leading directly to a particular page, view or section without starting at the homepage. On the web, a fragment such as #hours can identify part of a page. The destination should provide enough context to understand it and enforce the same access rights as ordinary navigation.

Reference: MDN : URI fragments · Source consulted 2026-10-18

In practice: open the link in a new window without navigating beforehand. Check the title, target section and routes to related content; if sign-in is required, check the destination after authentication.

Dependency graph

Representation of relationships between packages, modules or components used to analyze update impacts and risks. Distinguish direct and transitive dependencies and compare the graph with delivered software. A development module may differ in role from a production runtime component.

Reference: CycloneDX · Specification overview · Source consulted 2026-10-25

In practice: Find shared components and blocking versions before a major update.

Deployment

Process making a new website or software version available in a testing or production environment.

In practice: Prepare checks before and after release and a repeatable rollback.

Design token

Named reusable value applying a colour, spacing or size consistently across an interface.

Reference: Design Tokens Community Group : Format 2025.10

In practice: name the value by purpose rather than only its current colour or size.

Differential privacy

Statistical technique limiting what an analysis can reveal about an individual through mathematically controlled protection.

In practice: Define the analysis and required protection level before interpreting a noisy result.

Digital accessibility

The ability of a website or digital service to be used by as many people as possible, including people with disabilities.

In practice: test a real journey by keyboard, including reading order, labels and error messages.

Digital analytics

Collection and analysis of digital data to understand usage and improve decisions.

In practice: start with three decisions to make before creating more reports.

Digital product passport

Structured set of information associated with a product to document origin, composition, compliance or lifecycle.

In practice: Identify product data actually available and its owner before promising a complete record.

Direct answer

Direct, concise answer to a specific question, placed where readers can find it quickly. It retains conditions needed for accuracy and points to useful detail. Clarity supports reading but does not guarantee reuse by a search engine or appearance in an enhanced search result.

Reference: W3C WAI : Headings · Source consulted 2026-10-18

In practice: start a section by answering the question in its heading. Immediately include limitations that affect the decision, then explain further; avoid an absolute statement when the answer depends on a date, location or particular case.

Discover

Google recommendation surface that suggests content based on interests without requiring an explicit query.

In practice: Measure this surface separately from regular search and observe topics the audience truly values.

DKIM

Email signature verifiable using a public key in the signing domain’s DNS. It checks signed message parts and identifies the domain that applied the signature.

Reference: IETF : RFC 6376

Inspect the signing domain and validation result on a test message; the private key stays in the sending service’s environment.

DMARC

Mechanism connecting SPF or DKIM results with alignment to the visible From domain and allowing that domain to publish handling policy and report requests.

Reference: IETF : RFC 7489

Inventory legitimate streams and observe results with the email owner before strengthening the policy.

DNS

Distributed system publishing records associated with domain names, including addresses and mail information. DNS does not itself store the website’s pages. Distinguish the authoritative server’s response from copies held by resolvers. Cache lifetimes explain some temporary differences between visitors.

Reference: IETF · RFC 1034, Domain Names · Source consulted 2026-10-25

Source consulted : MDN · 2026-10-17

In practice: record the services depending on each record before changing it.

DNS TTL

Time to live, generally expressed in seconds, during which a DNS response may remain cached. It influences persistence of an old value after a change.

Reference: Cloudflare : Time to Live

Record TTL before a change and observe several resolvers rather than promising a universal propagation period.

DNS-01 challenge

ACME validation of domain control through a TXT record used for the challenge.

Reference: Let’s Encrypt : Challenge Types

Document the DNS owner and test TXT publication without copying credentials into the log.

DNSSEC

DNS extensions using signatures to verify response origin and integrity. They do not encrypt queries; an inconsistent trust chain can prevent validated resolution. Check delegation, keys and signatures together. A signed answer establishes neither a web page’s content nor its publisher’s business identity.

Reference: ICANN · DNSSEC · Source consulted 2026-10-25

Source consulted : ICANN · 2026-10-17

In practice: verify the validation chain and change procedure before enabling it.

Document version

Identified state of a published file linked to a date and exact content, distinguishing the current document from older copies.

In practice: attach an effective date and owner to the currently offered version.

DOM

In-memory document model organised as nodes that scripts can read and modify. The current DOM may differ from received HTML after results are added, a panel opens or another interaction occurs. Distinguish the initial response from this modified state when diagnosing a page.

Reference: MDN : Document Object Model · Source consulted 2026-10-18

In practice: inspect the rendered structure, not only source files, to find semantic defects.

Domain authority

Proprietary metric from some tools estimating a domain’s comparative SEO strength. It is not an official search-engine metric.

In practice: Treat this third-party score as a comparison clue, not an official ranking factor.

Domain name

Hierarchical name identifying an Internet destination, such as example.fr. It differs from a complete URL, hosting and a trademark; management should remain with the appropriate registrant. Separate domain, subdomain, path and parameters when comparing addresses; a similar name does not establish common ownership.

Reference: IETF · RFC 1034, Domain Names · Source consulted 2026-10-25

Source consulted : MDN · 2026-10-17

In practice: record the holder, renewal and services depending on the domain.

Domain ownership

Documented ability of an organisation to identify the registrant, renew and transfer its domain and manage DNS settings through authorised people.

In practice: check the registrant, renewal date, registrar and transfer procedure without sharing credentials.

Double booking

Two requests taking the same real capacity at the same time, often because the calendar or temporary slot hold is not synchronised.

In practice: try two simultaneous requests and an appointment change, then compare the site with the team calendar.

Download link

Link whose label makes clear which document opens or saves, its format and, where relevant, its size.

In practice: state subject and format in the link, then open the actual destination.

Drag and drop

Interaction allowing an on-screen element to be moved by grabbing and dropping it elsewhere.

Source consulted : W3C WAI : Dragging movements · 2026-10-09

In practice: Provide a keyboard method and clear feedback about the item’s final position.

Duplicate content

Identical or very similar content available at multiple URLs, potentially complicating selection of the reference version. Identify variants serving the same need before choosing a reference URL. Canonical signals should remain consistent with links and redirects.

Reference: Google Search Central · Canonical URLs · Source consulted 2026-10-25

In practice: identify URLs serving the same need and choose a consistent primary version.

Dwell time

Estimated time between clicking a search result and possibly returning to results. It is not provided as an official SEO metric.

In practice: Do not interpret an isolated duration without the task and how the measure is obtained.

Dynamic content

Content produced or changed according to data and context, on the server or in the browser. Identify what varies and when; personalisation also requires checking caching, access and signed-in state.

Reference: MDN : Server-side introduction · Source consulted 2026-10-18

In practice: Check rendered content when data is missing or slow to arrive.