What exactly is a FOAMIE?

I have been reading and some are talking about Faomies. What are they please, can anyone tell me?

It's the excess mucous and saliva your body produces in reaction to having something stuck in your pouch, with nowhere to go but up and out. You'll know it when it happens.

Thank you. Pretty sure I had one the pother day but it did not come out just all of the symptoms...yuck.