"I don't practice santeria I aint got no crystal ball.
I had a million dollars but i'd,
I'd spend it all.
If i could find that heina and that "sancho" that she's found,
Well i'd pop a cap in "sancho" and i'd slap her down." - Sublime from "Santeria"
By Ermentrude
Sancho
Spanish for the person who comes in your back door when you're at work, drinks your beer, watches your TV, and f's your wife.
I agree with all of the above definitions (which are basically the same), but thought it was interesting to note that instead of saying "salut" when someone sneezes, most of the guys I know say "sancho" instead, which I guess means that if you sneeze that means sancho is at your house with your lady.
Name used by fellow inmates for the guy that is fucking your woman and whom your kids are calling daddy while you are in jail. Most likely the person you think is your best friend or hate the most. Used in a heckling manner.