Very large wasp
That is a European hornet (Vespa crabro).
European hornets were introduced from Europe in the mid-1800's and have since become widespread in the eastern United States. The subspecies we have is originally from Germany and they are endangered in their native range as Europe has lost most of it's forests.
European hornets build paper nests like other yellowjackets and hornets. However, unlike bald-faced hornets, which build the large, exposed paper nests in trees, and yellowjackets, which typically build paper nests in the ground, the nests of European hornets are found in aerial protected areas, such as a hollow in a large, standing tree and sometimes in the wall voids of houses.
Like other hornets and yellowjackets, European hornets are attracted to fallen apples during the fall and can become pestiferous under fruit trees. Additionally, they strip the bark off of certain bushes (particularly lilac) during the fall to make paper for their nests, which can kill affected twigs and branches. They are also the only nocturnal wasp in the area and sometimes are attracted to porch lights, much to the dismay of homeowners that like to leave porch lights on at night.
The sting is quite painful - imagine a yellowjacket sting, but scaled up to size - and can cause localized swelling for a few hours. However, they are excellent predators and often kill bald-faced hornets and yellowjackets, so when homeowners find a nest but it isn't being too much of a nuisance (and no one in the immediate area is allergic to bee and wasp stings) I suggest they leave them be if at all possible.
For more information, please see this PSU fact sheet.