Glossary · Internet & Web

URI (Uniform Resource Identifier)

A URI is a string that identifies a resource by name, location or both; every URL is a URI, but not every URI is a URL.

Updated October 6, 2026

A URI (Uniform Resource Identifier) is a standardized string that identifies a resource, such as a web page, an email address or a book. A URL is the kind of URI that also says how to locate the resource.

Why it matters

The term shows up in specifications, APIs and frameworks, so knowing the difference prevents confusion. HTTP standards talk about request URIs, while everyday speech says URL. URIs that only name something, without a location, are sometimes called URNs.

Example

https://example.com/docs/intro   (URI and URL)
mailto:hello@example.com         (URI, not a web URL)
urn:isbn:9780141036144           (URI that names a book)

All three follow the generic scheme:rest syntax defined in RFC 3986.

Common misconceptions

  • Assuming URI and URL are different technologies; in practice you rarely need to distinguish them.
  • Forgetting that a URI can be relative (/images/logo.png) and only resolves against a base address.
  • Using unreserved-character rules inconsistently when building URIs by hand.

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