Samsung cellphone problems: What's a PUK and where can I find mine?

I just bought a Samsung SGH-a177 and i accidentally locked myself out of the phone. Now every time I press a on my phone tells me to "Enter PUK", but i have no clue what that is. So if you could tell me what that is and where I can find mine that would be great. FYI i have already tried 1234 and my the cell number w/ and w/o the area code.