n. (gee'ess'bee'em) Acronym: Greasy Shit Bowel Movement. A form of defecation similar to diarrhea that has more consistency and leaves a greasy film around the bowl afterwards. While easily confused with diarrhea, one can mark the difference by it's consistency which is more akin to pouring out a well made shit milkshake.
"Dude, could you use the brush after that massive gsbm? I think it's eating away the ceramic."
"Cancel all my appointments. A gsbm is brewing."