A link relation is an attribute that tells the relationship between the source and destination resources. This attribute is attached to a hyperlink to define the type of the provided link. Rel is short for a relation that specifies the relation between the tag and href whereas, href stands for hypertext reference. It is the main source of the file that tag use.
As the name suggests, the href rel attribute is a descriptive attribute that is used to specify the relationship between the current and the linked documents. This rel attribute is used only when href attribute is present.
The browsers such as Google Chrome, internet explorer, firefox, Safar, and Opera are usually supported by HTML <rel> attribute. You have to assign link, rel, & href to connect an external CSS file.