to thrum is the act of sticking ones thumb in anothers anal cavity and wiggling a little, either to pleasure or make a person very uncomfortable in your presense. Can be used intimately or as a form of socializing
Trevor and his boyfriend are thrumming enthusiasts and as a result both of them have loose bowels
by KingThrum August 31, 2008
A thrum is just between a throb and a hum. It's used to describe the throbbing hum produced by extremely loud, most likely live, music at an underground rave.
"Can you feel the thrum?"
by ateenangel August 09, 2006