I know what you are thinking, you see... I can read your mind, you could say I'm a telepath, or you could say I am sorcerer. But the generic term would be... a Psyker. 

There are many types of psyker's in the 40k universe and so I will guide you through several different types from the powerful and highly trained Librarians of the space marines to the strange and weird Zoanthropes of the bug like race, of the Tyranids.