Stalling is something poor sports do to annoy their opponent when it becomes clear they can't win. Stalling can be:
Letting the clock run out instead of resigning
Taking VERY long between moves, in effect letting the game run out but with some pointless moves added in.
People who do this will sometimes even send messages in chat telling their opponent what they are doing, such as 'haha, have fun waiting' and other similar things.
Stalling in Daily games is called 'vacation abuse.'
We know how frustrating stalling can be, and we don't tolerate it on our site!