I use the term "abstract" quite loosely, and I don't want to start any definition wars, so if you have something that YOU want to call an "abstract" image, feel free to post it here.
For me, an "abstract" is something that doesn't fit neatly into other categories, like "street," "landscape," or "portrait." It may or may not be a photograph of a recognizable object, but if so, the subject isn't what is important. If it is an interesting pattern, suggests something other than what it is, is evocative of some mood, or whatever, it's OK.
So hear are a few of mine in black and white to start things off.