"WikiSyntax" is the name for the codes that you enter in the text box, to cause different effects in an article.
For example, if you want italic text, you write it like so:
The word ''italic'' will be italic.
If you want bold text, you write it like so:
The word '''bold''' will be bold.
Headings are specified like so:
=== This is a Heading ===
A full list of the syntax can be found here: https://oddmuse.org/wiki/Usemod_Markup_Extension