1) Term used in music, particularly hip hop. It is a witty line, or slick rhyme.
2) A song by Felt
-That rapper spits hot bars, man! I love his rhymes.
-I spit hot bars, i spit on cop cars,
I spit game to the chicks that belong to rock stars,
Got the goods, uptown to Hollywood,
So what you don't like us, your girl probably would.
"Hot Bars" by Felt