A person of more than one racial background; usually looks quite distinctive from monoracial people
see also eurasian blasian biracial hapa etc.
real-life examples are everywhere, just look around.
When referring to an individual, a mixed person is someone who was born with two or more ethnicities.
I am mixed with Irish and Welsh.
We are a diverse school. This year's prom queen was mixed with Nigerian and Armenian.
Hienz 57 is a slang word (not actually a slur) for someone who is of many different ethnic groups.
Me I am part Mexican, Spanish, Italian, Irish and Japanese.
Or Tiger Woods who is every race White, Black, Asian, and American Indian. We would both be called Hienz 57.