It is a generic term used in the field of computing. 

• Identification of Resources: A URI identifies a resource either by location, or a name, or both. Such resources can be web pages (HTML documents), files, images, videos, or even services and databases.

• Syntax: The general syntax of a URI is a scheme, followed by a colon, and then a scheme-specific part. For example, in "https://www.example.com", "https" is the scheme, and "//www.example.com" is the scheme-specific part.

• Types of URIs:

URL (Uniform Resource Locator): A type of URI that, in addition to identifying a resource, provides a means of locating the resource by describing its primary access mechanism or 'network location'. E.g., "http://www.example.com/page.html".

URN (Uniform Resource Name): Another type of URI that identifies a resource by name in a given namespace, such as an ISBN for a book.

• Use in Various Protocols: URIs are used extensively in various Internet protocols, including HTTP (HyperText Transfer Protocol), FTP (File Transfer Protocol), and SMTP (Simple Mail Transfer Protocol).

• Standardization: URIs are standardized by the Internet Engineering Task Force (IETF) and are a fundamental concept of the World Wide Web.

• Encoding Rules: Certain characters in URIs need to be encoded (percent-encoded) if they are not allowed in that part of a URI. This includes, for example, spaces and some special characters.

Uniform Resource Identifiers are crucial in web technology as they provide a simple and extensible means for identifying and interacting with resources over the Internet.