Pure-blood
Pure-bloods are wizards and witches with a family tree devoid of Muggle members; or, at least, they have convinced themselves of this by removing any non-pure-bloods from their family trees. At the very least, one must have all magical grandparents to be considered pure-blood, though extremists would require no known Muggle ancestors. Thus, some would consider the children of Harry and Ginny Potter to be pure-bloods because all four of their grandparents — James and Lily Potter, and Arthur and Molly Weasley — were wizards and witches. Others, however, would consider them half-bloods because their paternal grandmother was Muggle-born, thus they have known Muggle ancestry.
Many pure-bloods consider themselves to be akin to royalty in the wizarding world, or at the very least the elite. They often disdain those of different blood status and Muggles, some even arguing that Muggle-borns should not be admitted into the wizarding world.
To be pure-blood is an uncommon trait, and their numbers continue to decline over time. There appears to be a continuous stream of new families entering the wizarding world as children from non-wizarding backgrounds with magical ability, and as a result those with long pure-blood lines are relatively rare. To maintain their "pureblood pedigree", some families have practised inbreeding, accounting for the mental instability of certain family members. Those same families tend to disown members who accept Muggles or Muggle-born wizards into their lives. These family members would be deemed "blood traitors".
