Stray can mean to wander from the right place (e.g. don't stray off the path) or to deviate morally (she promised to be faithful, but strayed with at least three of his golfing buddies, a caddy, the chaps in the pro shop and the club barmaid). In that case she could be described as straying or having gone astray (and no doubt called worse things by her husband!).
It can also be a person or thing which has strayed or become lost (I think this dog was a a stray). Stray is also some weird sciency thing which interferes with radio reception, or it can be something isolated or unusual (e.g. most bluebells are blue, but sometimes you see a stray white one).