What is BotNet....?

Botnet This is the name given to a collection of these bots.

Then what is Bot.......

Bots are software applications that run automated tasks over the internet. Bots perform tasks that are both simple and structurally repetitive, at a much higher rate than would be possible for a human editor alone. Bots are used in a malicious way by criminal gangs to coordinate attacks on networked computers for financial gain. (Thousands of infected PC's around the world can all be used at the same time for an unlawful act.)