Newbie question: What is an airdrop and are they worth participating in?

[zikabra]

I see people asking about airdrops all the time.

What are they and how do you figure out if one is worth participating in?

Why not?
Every new token you can get for free is worth of trying because you don't have anything to lose and you could earn something. Please be careful on those airdrops which doesn't come for free and avoid them because if you have to pay to get them it is most likely initial coin offer.