I don't understand words during conversations.

I've been feeling this way for some time now and its just that everyone seems to understand each other but I don't and have to ask. Basically me and my friends will be having a chat and one of them will use a "big" word as I would call it and everyone else knows what the word means and because I don't I have to ask which makes me feel really stupid it and they have to give me a simple explanation of what it means.

It isn't even just for words but for some many other things like what is currently happening in the news etc and it just makes me feel really excluded in the group. It seems like I've missed some sort of general knowledge that everyone else has.

I was quite a failure in school but I'm great in college perhaps that's why?