fetish: A strong sexual interest in or obsession over some object, body part, or activity. Examples include foot fetish and latex fetish. Also used broadly to describe any non-traditional sex, especially BDSM.
solo: Can be a video with just one performer, often masturbating or flashing. Solo can also be associated with another term, like "solo female" - a girls only scene, or "solo male".
masturbation: Images of self stimulation particularly the genitals - see toys.