A URI, or Uniform Resource Identifier, 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: URLs (Uniform Resource Locators), which indicate where a resource is located, and URNs (Uniform Resource Names), 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. For example, a URI like https://www.example.com points to a specific website, while a URN might identify a book by its ISBN. Understanding URIs is fundamental for web development and information retrieval.