Dabbing is doing the dab dance move
Dabbing, or doing the dab, is a dance move in which the dancer simultaneously raises his arm and elbow while dropping his head. It looks like you are sneezing in your elbow.
Even though the dab is still very popular, it has been around since the beginning of 2015. Cam Newton‘s (a football player) started the dab movement by doing his dab move after a touchdown against the Titans.
Betty White teaching you how to dab
https://www.youtube.com/watch?v=GATJnZKYPDg&rel=0