What is a Canonical URL?



A canonical tag (aka "rel canonical") is a process of informing search engines that a particular URL describes the original copy of a home page. Doing the canonical tag stops difficulties created by same or "duplicate" content arriving on various URLs.
 
Canonical URLs relate to the concept of selecting the best URL for the web pages that the visitors want to see. Also, known as Canonical tags, these URLs help in content syndication when multiple versions of a same page become available over the Internet. Thus, it is used to resolve issues related to content syndication.
For example:
Example Domain
example.com/
Example Domain
example.com/home.asp
All these might look same, but technically all are different URLs.
 
A canonical URL refers to an HTML link element with the attribute of canonical found in the element of your web page. It specified to search engines your preferred URL in the other words if you have a web page accessible by multiple URL or different pages with similar content. A canonical tag is a way of telling search engines that a specific URL represent the master copy of a page.
 
Thanks to all valuable members for giving the answers with their great experience but I would like to know the others use of this canonical URL apart tell search engines about duplicate pages on a website?
 
A canonical URL is the URL of the best representative page from a group of duplicate pages, according to Google. For example, if you have two URLs for the same page (such as example.com? dress=1234 and example.com/dresses/1234 ), Google chooses one as canonical.
 
To explain it as briefly as possible, a canonical URL is the URL of some page on the site that Google thinks is most representative from a set of duplicate pages that also exist there. For example, if you have more URLs for the same page, algorithms will choose the most representive ones and decide that that will be the main URL of that specific page.