what is 英语四级?

hey,i just took a view of the E group .i am so surprised that sb always focuses on 英语四级 subject.so it takes a question out from my mind.is 英语四级 a kind of books or E level?why does my teacher never tell me about it?r there some levels just like 英语四级 in college?who can definitely tell me what 英语四级 is?
thanks a lot!

what is 英语四级? could u tell me what 英语四级 is? what is behaviour？what is Organisation Behaviour? what it is?/what is it? What is love? what is like? What is WINS？ What is 对冲基金? what is BT? what is love kin is what???