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.
Hey man, lets spit bars on this new beat!
by DirtyD-Damnit June 26, 2014