Definition and Usage
The <link> tag defines the relationship between a document and an external resource.
The <link> tag is most used to link to style sheets.
Tips and Notes
Note: The <link> element must be embedded in the head section, but it can appear any number of times.
Differences Between HTML and XHTML
In HTML the <link> tag has no end tag.
In XHTML the <link> tag must be properly closed.
via HTML link tag.