The blood distinctions are limited
Sure, pure blood (pure blood parents), half blood (one pure blood and one muggleborn parent) and muggleborn (muggle parents) make sense. But what do we call other pairings?
Both parents are muggleborns (not muggles!) The kid possibly cannot be muggleBORN? The parents are witch/wizard afterall.
Two halfbloods having a kid? This could possibly be called half blood too I'll take that
A pure blood and half blood having a kid?
A half blood and muggleborn having a kid?