Spam is a form of internet trolling and can consist of many types, including posting the same message over and over, repeatedly posting the same image or typing gibberish. It is a very large problem throughout the internet, Chatango being no exception. Many spammers are also know to be able to change their IP, which makes them difficult to eradicate.
On pretty much every chat on Chatango, there is a rule against spamming. Even with chats that don't have spamming, you can be kept from posting messages if you post too much at one time. In PMs, you will be disconnected if you post too much in a short amount of time. Slow Mode was created to further prevent spamming, at the price of keeping others from posting in a short amount of time, too.