From WikiTemp, the GBAtemp wiki

BBcode (acronym for Bulletin Board Code) is a way to add Formatting to your text on Forums. Just like with HTML, the BBcode must be wrapped around the text it needs to change. The only difference is that BBcode uses [ ] tags instead of < > tags.

Some Examples

BBcode Result
[b]Text[/b] Text
[i]Text[/i] Text
[u]Text[/u] Text
[s]Text[/s] Text
[url=""]GBAtemp[/url] GBAtemp
[color=red]Text[/color] Text
[background=red]Text[/background] Text

Full list of BBcodes

The very full list of available BBcodes can be found here. You should really take a look at it!

Thread talking about BBcodes

Several users take time to create BBcodes lists:

BBcode list by tj_cool

The BBCode Thread by Densetsu