I am sorry for not providing enough details. Nikah is a kind of procedure, analogous to the christian church procedure where priest makes the marriage lawful by christian rules, but instead the priest, we have mullahs, and instead of church we have mosques( Though if I am not mistaken, my parents had their nikah at home, which is also considered ok at least in our country). I think the wikipedia page would be the most unbiased source for you to check out if you are interested:
http://en.wikipedia.org/wiki/Marriage_in_Islam
I'm sure I'm missing subtleties, but it might help other readers to think of 'marriage' or 'marriage contract' etc..
I wasn't sure what to make of it and thought for a second that it's an accessory or something like that.