A URL (Uniform Resource Locator) is defined as a globally recognized address for documents and resources located across the World Wide Web  , such as web pages, text files, graphics files, a particular program, application, or other types of resources available Over the Internet,  a URL is referred to as a web address, and this address is used by Internet users by typing it directly into the address bar of any of their web browsers, or by clicking on a hyperlink on a web page, or Within emails , or even from an app. 
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The URL is always visible at the top of the browser window, specifically in the address bar, and it is visible in most browsers of smartphones and tablets, but it disappears on these devices when you go down the open web page through the browser, and if the URL is not completely visible For the user, it can be fully shown by clicking on the domain name that appears in the address bar. 
The URL consists of several parts, each of which expresses a specific piece of information, as follows:
The Scheme is the first part of a URL that the address begins with, and this part is also known as a protocol. The schema or protocol indicates the type of address that the browser must properly connect to and thus enable it to access the page or resource it is expressing. URL,  , There are many types of protocols or schemes by which web pages can be accessed, but for normal browsing, both Hypertext Transfer Protocol (HTTP) and Secure Hypertext Transfer Protocol are usually used. Which is referred to by the acronym (HTTPS).  
The web browser usually hides the type of protocol used in the URL, and there is no need to type the protocol name or schema when typing the URL, because modern web browsers fill this field by themselves when typing the URL,  It should be noted That the name of the protocol used in the URL is followed by a colon and two forward slashes before writing the second part of the address, as follows: 
The domain name or domain name is the most visible part of URLs, as this part refers to the name of the website to which the URL refers, and all web pages on one website share a unified domain name for all of them,  and includes The domain name has three main parts as follows: 
Subdomain: (subdomain), the subdomain is considered a generic symbol for all resources on the World Wide Web and is referred to by the symbol (www), however this symbol can be specified to be specific to fetching a specific type of resource such as videos.
Domain name: (domain name), which is the actual name of the site to be visited through the URL, and this part of the address is unique and distinctive; Each website has a different domain name than any other website on the web.
Top level domain : (Top level domain), referred to by the abbreviation (TLD), and this part is concerned with specifying the type of content contained in the website you want to go to through the URL. Commercial websites are referred to as the top-level domain (.com), while Enterprise websites are referred to as a top-level domain (.org).
It is worth noting that the three parts of the domain name mentioned with the symbol (.) are separated as follows: www.mawdoo3.com.
Port is defined as a reserved channel over the Internet for specific purposes, where the port is related to the type of protocol used in the URL; Port 80 is used in Hypertext Transfer Protocol (HTTP), while port 443 is used in HTTPS, each web browser must connect to a specific port in order to access resources through a particular website. 
The path is defined as the resource to be accessed within the website associated with the URL, as the path tells the browser used to load a specific page, such as a video, image, text, or other resources available on the site, and the term (Edit) indicates if Its appearance in the path name indicates that the URL leads to a page that can be written and edited, while the term (Videoplay) indicates that this page is related to playing a particular video.  
URL Validity Terms
When writing the URL, it is required that it only consist of a set of: alphabetic characters, numbers, in addition to a set of symbols, which are as follows: 
Exclamation mark ! .
Dollar symbol $ .
Police symbol - .
Underscore symbol _ .
Plus sign + .
The apostrophe symbol ' .
The star symbol * .
The left and right bracket symbol ( ) .
URLs that are used by Internet browsers can be classified into two main types, which are as follows: 
Absolute URLs: URLs that contain all the information needed to locate a particular web page or resource on the website.
Relative URLs : This type of URL contains less information about the page to be accessed.
URL shorteners is a technique through which a URL can be shortened and made shorter while keeping it directed to the same requested page across the web . : Rebrandly, Budurl.com, and many other services, some of which are freely available online.