Why are NP problems called that way (and NP-hard and NP-complete)?

Question

Really.. I\'m having the last test for graduation this Tuesday, and that\'s one of the things I just never could understand. I realize that a solution for NP problem can be

Answer 1

NP is called NP (nondeterministic polynomial time) because an NP problem can be solved in polynomial time by a nondeterministic turing machine.