An "Air Drop" is when a cryptocurrency (usually a new one) gives away free tokens in their currency. Sometimes they award these to owners of a different coin or token. Other times, like in the case of all listed below, it's to get the word out.
FREE COINS & TOKENS!
Robotix (3/26)
Use "howdycrypto" for referral
http://bit.ly/airdrop-rbtx
CloudBounce (3/31)
https://www.cloudbounce.com/dbounce?r=ryh31dvKf
House Panda (3/31)
t.housepanda.eu/hodl2bot?start=AARON2OPG
Valorem (4/1)
https://advalorem.io/airdrop/
Invox (4/10)
https://airdrops.invox.mo.works/sign-up/qh294i
CCRB (4/27)
https://ccrb.io/affiliate/986225
Pharmz (5/1)
https://pharmz.io/invite/?id=hiLwdqYQ