What is a canonical url?

@clarabelle 

A canonical URL is a way for webmasters to tell search engines which URL is the preferred or "canonical" version of a web page. When there are multiple pages with similar or duplicate content, using a canonical URL can help to avoid confusion and ensure that the right content gets credited by search engines.

For example, if you have two pages with the same content, one accessible via "example.com/page1" and another accessible via "example.com/page2", you can specify which one you want to be considered the main or original version of the content by using a rel="canonical" link in the HTML header of the page. The canonical URL would then be "example.com/page1".

This helps search engines to understand which page is the preferred one to be indexed, and to avoid indexing the same content multiple times, which can negatively impact search engine ranking.