A URL is a Uniform Resource Locator.
The first part of the address is called a protocol identifier and it indicates what protocol to use (eg. http or ftp), and the second part is called a resource name and it specifies the IP address or the domain name (eg. website.com) where the resource is located. The protocol identifier and the resource name are separated by a colon and two forward slashes. (eg. http://website.com)
For example, the two URLs below point to two different files at the domain website.com. The first specifies a document file that should be fetched using the FTP protocol; the second specifies a Web page that should be fetched using the HTTP protocol:
ftp://www.website.com/stuff.doc
http://www.website.com/index.html
EDIT:
URL - Uniform Resource Locator
Something called a Uniform Resource Locator (URL) is used to address a document (or other data) on the World Wide Web. A full Web address like this: http://www.w3schools.com/html/lastpage.htm follows these syntax rules:
scheme://host.domain:port/path/filename
The scheme is defining the type of Internet service. The most common type is http.
The domain is defining the Internet domain name like w3schools.com.
The host is defining the domain host. If omitted, the default host for http is www.
The :port is defining the port number at the host. The port number is normally omitted. The default port number for http is 80.
The path is defining a path (a sub directory) at the server. If the path is omitted, the resource (the document) must be located at the root directory of the Web site.
The filename is defining the name of a document. The default filename might be default.asp, or index.html or something else depending on the settings of the Web server.