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.