Telepathy is a type of ESP that allows the user to read the thoughts of others, implant suggestions and change thoughts, control others, and even locate others using their mental signiature, plus many other uses.
In the ancient ANCIENT times (Caveman era.) before there was a language or easy way of communication, humans developed this ability which some beleive to have kickstarted evolution of other ESP and thus Psychokinesis. Since then it has been further trained and adapted in secret to become what it has today. It is also widely used by animals of all types.
There are many MANY uses for Telepathy, such as mind reading, direct control of others, forced hallucination, look through someone elses eyes, subliminal commands, information and memory download just to mention a few.