Definitions beginning with U

UI

User Interface: visual and interactive components through which a person uses a digital product.

In practice: Check component labels and states in a full journey, not isolated screens.

Unique visitor

Estimate of distinct people or devices visiting a service during a given period.

In practice: Read the identification method and its limits before presenting this count as exact people.

Unit of measurement

The reference giving a value meaning, such as seconds, euros or kilograms. Publish it with the quantity and context; distinguish counts, percentages and denominators before comparing values.

Reference: Schema.org : QuantitativeValue · Source consulted 2026-10-18

In practice: state the unit and denominator for every percentage.

Upload

Sending a file from a device to a server or remote service. Selecting a file in a form does not establish transfer or acceptance. The journey should distinguish selection, any progress, receipt and validation, explaining errors without implying that the recipient already has the document.

Reference: MDN : File input · Source consulted 2026-10-18

In practice: try an accepted file, a rejected format and an interruption. Check stated limits, the final message and recipient-side receipt using fictional data; a progress bar reaching 100% is insufficient.

Uptime

The share of time a service is considered available under a defined rule. State period, check frequency and exclusions; an accessible homepage does not prove booking or contact works.

Reference: Google SRE : Service level objectives · Source consulted 2026-10-18

In practice: Examine the measurement window and incidents users experienced, not just a monthly average.

URL

Uniform Resource Locator: address identifying a resource location and the protocol used to access it.

In practice: check that the address can be shared, understood and resolves to the intended resource.

URL inspection

Check of a specific URL to examine accessibility, canonical version, indexing and information known to a search engine.

In practice: Inspect the exact URL after a fix to check retrieval, indexability and detected canonical.

URL parameter

Information in a URL query string, often as name=value. Handle encoding, repeated names and missing values explicitly; avoid placing secrets or sensitive data there.

Reference: MDN : URLSearchParams · Source consulted 2026-10-18

In practice: Test possible combinations and avoid creating equivalent pages without need.

URL rewriting

Internal or external rewriting of addresses to present readable URLs or route requests to the proper process.

In practice: Test old addresses, internal links and final statuses after the change.

Usability

Ease with which users can understand an interface, complete tasks and avoid or recover from errors.

In practice: Observe someone completing a task and record hesitation without guiding them.

User agent

Software acting for a user during a Web request, such as a browser, crawler or screen reader.

In practice: treat the declared string as a clue and cross-check other signals when identity matters.

User flow

Sequence of steps and decisions through which a person completes a task. A user flow includes errors, backtracking and possible outcomes as well as the ideal route. It helps check continuity between information, action and confirmation across the screens involved.

Reference: W3C WAI : Complete processes in evaluation · Source consulted 2026-10-18

In practice: start from an emailed link, complete the task using a keyboard and check its confirmation. Repeat with an input error and a backward step; one accessible screen is insufficient if the full process remains blocked.

User-generated content

Content contributed by a service’s users, such as a review, comment or forum reply. Its origin does not remove the need for contribution and moderation rules. Authorship, publication, reporting and abuse handling should be distinguished to preserve useful exchanges.

Reference: Google Search Central : Prevent user-generated spam · Source consulted 2026-10-18

In practice: submit a fictional contribution and then a report. Check requested information, visible status and responsibility for responding. Plan for spam, unwanted links and corrections without implying editorial endorsement of every message.

UTM parameter

Parameter added to a URL to identify a link’s source, medium or campaign in a measurement tool.

In practice: Use a short naming convention and check that parameters do not fragment canonical URLs.

UX

User Experience: overall experience before, during and after using a product or service.

In practice: observe a whole task (find, understand, act and receive confirmation) rather than a single screenshot.

UX writing

Design of interface text to clearly guide action, explain a state and reduce hesitation.

In practice: Test labels and error messages in the real journey with someone unfamiliar with the product.