Bandwidth in this situation is literally the amount of data you have downloaded.
Anything connected to the internet will download data, it just depends on what you are doing that determines how much.
For example if you are actively downloading (mp3s, films) then you will quickly rack up a lot of bandwidth, as you are pulling data as fast as possible continuously.
If you are browsing, then very little will be used (just enough to load some text and graphics every few mins).

Playing online games (ps3) will be a fair amount, but not massive - unless of course you are downloading games/patches/updates etc.

What is your allowance?