look up any word, like donkey punch:
 
1.
upon climax (either self-induced through masturbation, or with a partner) one covers half of the penis hole with the thumb to increase internal pressure in an effort to maximize the velocity and thus distance of the ejaculate.
"hey kasko, how far did you shoot the load after you half capped it?" "dude it went like 20 feet!"
by hairy potter July 10, 2004
 
2.
A term used to describe a decapitation that doesn't remove the victim's entire head--often removing only from the nose upward. The half-cap is commonly seen in slashers or other horror films.
"OMG, dude! Did you just see that half-cap?! Freaking nasty..."
by Count_Claudio February 03, 2012