Do trust funds gain interest?

I just discovered my grammy's will and it notates that she set aside money for my cousin and I in seperate trusts. My question is this - do trust funds earn interest? I don't know what type of account it is in exactly, and I dont get it until I'm 25 (another 5 years). It was created in 1990 so if it did gain interest, I would have quite a few years worth, that is -- if there is interest. It'd be nice to know! :)