In reference to rapping in the studio or freestyle rhyming "bars" indicates the words used in the number of lines in a 4 count beat. The Majority of Rappers "spit" or say these rhymes in 16 counts of 4 beats. If a rapper suggests spitting bars he will most like try to prove his/her superior ability to rhyme and with clever and witty use of language. Usually ending with "BARS!" to indicate completion of their 16 Bars or one complete hiphop verse.
John:"yo ro's a bitch"
Ro:"oh yea, wanna spit some bars"
John:"yo check it, you a bitch, I put you in a ditch, your a pussy and your mom smells like badussy"
Ro: "True"
