When a person becomes a member of a certain gang they must kill a designated person in order to join said gang (blood in) and the only way out of the gang is to die (blood out)
"Why can't juan get out of the hood?"
"The only way out is death, his gang is blood in blood out."
by Al Johnson September 12, 2006
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A therm related to gang culture.

Blood in . To get into a gang, you got to spill some blood, usually murder.

Blood out - The gang is for life. The only way to get out is to die.
-Man, Don't mess with those guys, they're blood in, blood out.
by Amys April 5, 2006
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