The document discusses URLs (Uniform Resource Locators), which are the complete addresses of websites. Each webpage has a unique URL address. A URL is made up of several parts, including the protocol (such as http or https), domain name, sub-domain, and file name. The most common protocol for webpages is HTTP, which stands for Hypertext Transfer Protocol and is used to transfer pages on the web. Some sites use HTTPS to add encryption for security. The domain name uniquely identifies a website. A sub-domain is a subdivision of the domain name and usually includes a country code. The file name specifies the requested document.