A half rhyme is when a rapper says a word but changes the actual pronunciation to make it rhyme with the other lyrics. Especially in the song "oh yeah" by lil' scrappy. Where he rhymes "eyes" with 'tires' but really says "thighs"
"i was listening to Oh yeah the other day. and i just figured out that the official lyric is tires instead of thighs."
"oh i know, biggest half rhyme i have ever heard."