What is an oversize vehicle?

So I have a U-Haul trailer, that is smaller than a sedan, in a parking space I paid for. The owner of the condo i live in said that it has to be moved because it is an oversize vehicle. I'm pretty sure he is just doing this because I told him to move some snow blocking the space, that he put there. Now he's mad at me and this is how he is getting me back. But anyways, how can I prove it is not an oversize vehicle, and prove it is legal for me to park there?