What does expunged mean exactly?

I was arrested in Jersey City, New Jersey and had it expunged. So does that mean I don't have a criminal record? Does that mean I'm still clean? From what I hear it means that a person has no criminal record at all. But I find that hard to believe. I got it expunged but it still worries me. My family tells me I shouldn't worry because I had it expunged and its like it never happened. It that true? How does it effect my life if its expunged? I know if I apply for a law enforcement job I have to tell my employer about it.