URL stands for Uniform Resource Locator. It specifies the global address of web documents and web resources. The basic reason behind locating or identifying a resource on the web is access or communication. Interaction between web users and the Internet resources is possible, only if each resource on the Internet is identified in a standardized manner. A URL serves this purpose. Let's look at the different parts that compose it and what purpose each of them serves.
The first part of the address is the protocol identifier. HTTP and FTP are examples of protocol identifiers, which indicate the protocol in use. More rightly known as the scheme, this part of the URL denotes how to connect to the web resource. It is not case-sensitive but the canonical form is lowercase.
The second part of a URL is the resource name that comprises the IP address or the domain name of the web resource. It denotes where to connect. The domain name may be followed by a port number which is separated by a colon. When specified, a connection to that port number is established. If the port is not specified, the browser connects to the default http port which is 80.
The domain name may be followed by a path when a particular resource such as a file or a page needs to be retrieved. This part of the URL specifies what to retrieve. It is case-sensitive. On servers based on Microsoft, it is not. A URL may consist of a fragment identifier which denotes a specific location on the page. If it is a part of the URL, the browser displays that specified part of the page.
A uniform resource locator is synonymous with uniform resource identifier that is abbreviated as URI. By definition, URI is a string of characters that is used to identify resources on the Internet. Either it is the uniform resource locator or a uniform resource name (URN).
Typically, HTTP is the first part of a URL. As you know, it is the protocol identifier. It is followed by a colon and two forward slashes after which comes the domain name of the resource to be located. URLs are commonly referred to as website addresses. To reach any particular website, you need to type its URL in the address bar of your browser, which then retrieves the desired page for you.
An internationalized resource identifier (IRI) is a type of URL that includes Unicode characters. It allows one to create URLs using one's local alphabet. The domain name is known as an internationalized domain name (IDN). It is converted into punycode, wherein Unicode characters are represented as ASCII characters that DNS supports. When a user specifies a URL in the local alphabet, it is converted to Unicode, and characters that are not a part of the URL character set are converted to English letters using percent-encoding.
Tim Berners-Lee and the URI working group of the Internet Engineering Task Force (IETF) standardized the Uniform Resource Locator in 1994. The Domain Name System created in 1985 was combined with the file path syntax.