Origins: Lewis Carroll's "The Hunting of the Snark" (1874)
Witty sarcasm, used to belittle someone or something without becoming ad hominem. Also used to describe practical jokes of a particularly funny and sabotaging kind.
Snarky refers to a concise, clever comment that's referential to something. It's normally jagged, like sarcasm, but it involves more creative thinking than a sarcastic comment does. It can be in reference to something from popular culture, or a turn-of-the-phrase that creates something original from it's source material.
You're sitting on an airplane, with a family full of annoying young children seated behind you, who are kicking your chair, being noisy and generally irritating...
You turn to the person seated next to you, and say in a snarky fashion: