Onomatopoeic word commonly used in context of two things bumping each other, particlarly small things. It has less of a metallic connotation than "chink" or "clunk" and tends to imply a light-weight object or group of objects.
Some feel it is a perfect word to refer to the tell-tale sound of Scrabble tiles in a bag. Anyone who has played a round of the popular crossword game would recognize the distinctive plink of wooden tiles colliding as a hand searches for the three best random letters, there at the bottom... no, to the right... THERE! Those are the ones I want.
In the online world, it has become a proverbial "mating call" for those looking for opponents to partake in online Scrabble-like word games such as Yahoo! Games' Literati.
Please do not confuse with plunking!
According to Jurph, "plink" is also a United States Air Force slang used to describe casual attacks on armored targets, usually indicative of an easy single-shot, single-kill situation. This sense is almost definately related to plunking.