The word bot comes from robot. Bots are programs which connect to an IRC server and perform commands you tell
them to do. Most bots are very configurable and can be expanded with scripts. The main purpose of bots are to
guard channels. On IRC servers without ChanServ a channel is removed when nobody is on them. When you have a bot
which is permanently online you can put it in the channel to prevent it from being removed.
Bots can also store information about people who are not allowed in the channel
and kick/ban them when they join. This way you don't have
to do everything yourself and also have a channel that can't
be taken by someone else just because he/she joined while
nobody was around.