I learned about this word today too. It stands for 'Joy Of Missing Out".
You were thinking of buying a coin and later that coin dumps to oblivion. That's JOMO!
Happened with once or twice back few years when there was project who was in hype and the coins were in demand so as profit motive I also wanted to invest in it but didn't have the money at the time so was feeling bad but later on the project team abandoned it due to which the coin lost it's major stake and investors looses all their funds.So have also came across new word now JOMO.