Spam on the internet started initially with email, and most of the definitions you'll find online are in regards to email and usenet groups. The definition has expanded with the advent of posting boards. Basically, spam in email is unsolicited advertisements. They can be a one-time mailing, or can "flood" your inbox. On bulletin boards, spam is not just about advertisements. Posting several new topics within a short period of time, thus "flooding" the board, is also considered spam. Many sites simply discourage spam, while others will not tolerate spamming in any form and will ban spammers without warning.