The hardened deposit of semen left in the male urethra after masturbation or intercourse. Usually formed when one doesn't "clean the pipes" after such activity resulting in a temporary blockage that can lead to random urinary problems and sometimes temporary pain.
Dude, I forgot to piss after whackin' off and now I got a wicked cum-plug. I just accidentally pissed all over my bathroom.
The dried seman that accumlates at the tip of man's urethra after sex. During the man's first post-coital urination, the urine stream will go in erratic, unpredictable directions until the cumplug is burst.