The act of two males rubbing their genitals together for the purposes of stimulation
The gay male version of 'scissoring'
man look at this guys go... They're really frotting (frott) away on eachother.
When a man or woman rubs their genitals on another person, often without consent. This may be with or without clothes on, and may or may not be deliberate.
When getting onto a packed train you 'accidentally' frott the woman in the red dress.
When leaving the window seat on an aeroplane you frott the people sitting in 37b and 37c.