The term “8 bars” is an actual reference to a type of measurement used by famous rap artists like Jay-Z and Eminem. 8 bars might refer to a shortened verse by a rapper that does not require a lengthy lyric to slay or drive hard. 16 bars is the usual measurement for a verse and 8 bars imply that they are only half yet packing a punch. You might hear this:
“I’m just gonna need an 8 bar to destroy this fool!”
“Eminem’s diss track has this 8 bars that decimate Machine Gun Kelly.”
This term is still well-used to this day and is often reserved for nasty rap verses of some greats.