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3.
A Half Blood is the stage inbetween a boner and a floppy.
"Damn, that ass just gave me a Half Blood"
by qwertywtfbbqomg May 04, 2005
 
1.
Half Blood is a term for a witch or wizard that has 1 magic parent and 1 Muggle parent. Most of the wizarding world is either made up of half bloods or muggle-borns. There is no derogatory term for half bloods like there is one for muggle-borns (mudbloods). So the purebloods that think they are better than everyone else, can't call them a bad name.
Seamus: im half-and-half. dad's a muggle. mum's a witch.

Dean: yeah im half blood. my mum's a muggle and my dad's a wizard.
by gryffindorseeker16 December 01, 2011
 
2.
Someone who is half descended from one race.
Dave's mother is Russian, and his father is Canadian, so he is a half blood.
by DuncanD May 26, 2011