Trashcore is an aesthetic based around decaying, abandoned buildings and general garbage. Anything old, poorly made, broken, or just generally gross and probably not safe to be around could probably qualify as trashcore.
Trashcore fashion is very similar to crustpunk. There isn't a sense of anarchy to trashcore, but ripped clothes that are either homemade or from the thrift shop are common. White t-shirts with doodles or weird phrases scribbled on with marker is something you'll see in trashcore. You'll also see a lot of references to opossums and rats.