Refers to da friendly wave, nod,. smile, etc. dat you courteously preform in response to a passing motorist/pedestrian who honks or calls hello to you, but you are unable to identify said greeter because the person has already moved too far away by the time you "get turned around" to see who it was.
A sportsman friend of mine experienced a classic case of "generic greeting" whenever he visited my area --- "The only thing I can figure is that I must have a vehicle that looks a lot like a local resident's, because everyone waves eagerly to me when I drive through town, and yet I don't really know anyone here. But heck, that's perfectly okay with me --- I dunno why they wave, but I just always wave back!"
by QuacksO August 5, 2019