Bandwidth in bit/s may also refer to consumed bandwidth, corresponding to achieved throughput or goodput, i.e., the average rate of successful data transfer through a communication path.
Basically, all the data sent back and forth is classed as bandwith. When you rent webspace or a web server, you get a set amount of bandwith. If this limit is reached, the forum would go down until the next monthly cycle begins or we pay more. So its not about space as such in terms of the amount of sections on here, but the amount of posts and visits which uses bandwith by sending the data back n forth.