1) used to describe stopping by your friend's work at random hours of the night just to say hi.
2) an unexpected visit from someone (maybe a stalker) who has a crush on you.
1) Last night, Mike showed up at work around midnight for a stalk by. It freaked me out!
2) MW: I'm going to be bowling tonight, what are you doing?
RC: not much man... just working... stalk by after bowling?
MW: you bet!