What is a WAD?

Whats a Wad or wad file? I ask because i see this word come up alot in youtube/wii soft mod vids and other places.Also, In my research, i find that WAD/s are often associated with a ban, Why is that?
Thanks alot and srry for the newb question.

A WAD is simply a container used to hold system files. WADs are the most convenient (essentially the only) way to distribute IOSes, system menus, custom channels, and pirated Wii Ware and Virtual Console games. Most commonly, when people talk about WADs, they are talking about pirated WW/VC games. For this reason, WW/VC WADs are prohibited here. However, other WADs are allowed, provided they are obtained legally (they almost always are).