A Uniform Resource Identifier (URI) is a string of characters used to identify a resource on the internet. It provides a way to access resources, such as web pages, images, or files, by specifying their location or name. URIs can be categorized into two types: Uniform Resource Locators (URLs), which indicate where a resource is located, and Uniform Resource Names (URNs), which identify a resource by name in a specific namespace. URIs are essential for web navigation and communication, allowing users and applications to locate and interact with resources efficiently. They are a fundamental part of the World Wide Web and are used in various protocols, including HTTP and FTP, to facilitate data exchange and retrieval.