An HTML Anchor is a name for a point on a page formatted in HTML.
The anchor template special:anchor allows you to add HTML anchor tags (<a name=''>) to a wiki page. This can be useful to have named (and stable) link targets.
The template has one anonymous parameter: the name of the anchor.
Format: the anchor name has to be a valid wiki pagename, i.e. no spaces, only chars and numbers. The anchor name must not use names which are generated automatically (e.g. 'diag12', 'toc3', 'r4', '2'.) Furthermore the anchor name must not start with an uppercase letter (lowercase letter or number is fine.)
{{special:anchor | coolSection }}
results in
(well there's nothing to see here, but if you look at the HTML code[1], you see the anchor being inserted :o)
Once an anchor is defined you can link to it, like you link to other HTML anchors in the page:
See also Linking to parts of pages on the page Text Formatting Rules.
[1] Try selecting the text around ‘results in’, right-clicking and choosing ‘View selection source’.