Linux terminal language learning?

I need to learn the computer language used in the terminal of the Linux ISO, more specifically the back-track linux. Can you include some links where i can learn this language. If I'm not mistaken it's UNIX, but i do not know if it's a more modern version or a copy of it, as UNIX is quite old. What is this language called and please include sites where i can learn it. Thanks! (Bdw 10 points best ans!)