It's an abbreiation for the phrase "Ultimate Mind Fuck". It can have 2 possible meanings:
1. when 2 people unite mentally as well as physically during sex. This is implicated in the 1993 song "UMF" by Duran Duran. The terms "UMF" and "Ultimate Mind Fuck" are not in the lyrics.
2. brainwash, mass deceit, censorship, when several people (as in a cult or an entire nation) are mentally manipulated and hoodwinked and led astray by propaganda, corruption and outright lies and absolute bullshit.
1. Renee and Angela made love last night and experienced union in body and mind. They shared the UMF.
2. In the 90s decade there was a lot of New Age "solutions", shilling evangelists, superstitions, comet cult suicides, Y2K hysteria and other end-of-the-millenium bullshit. Then came the 00s with all its corruption, stupidity and shit and the Iraq war circus. That's one major UMF after another!
Ultra Music Festival which is an anual Electronic Dance Music and is one of the most popular and most recognized EDM festivals where the mosf popular EDM Dj/Producers perform live to a massove crowd.