Wiki markup, also known as wikitext language and wikicode, is a lightweight markup language used to write pages at wiki-based websites like fandom or wikipedia, that is a simplified/alternative/intermediate to HTML. Its ultimate purpose is to be converted by wiki software into HTML, which, in turn, is served to web browsers.
There is no commonly accepted standard wikitext language. The grammar, structure, justification, keywords and so on depend on the particular wiki software used on the particular website.
Different Wiki programs may support use of different sets of HTML elements within wikitext. In some cases, permitted HTML elements may be configured by individual wiki sites. MediaWiki supports many common HTML tags.