In jazz, the head is the composed theme of a tune, the recognisable melody with its chords. A typical small-group performance follows a “head-solos-head” plan: the band states the head clearly, then each soloist improvises over repeated cycles of the same chord structure, and finally the head returns, sometimes with more freedom than the first time. One complete pass through the form is called a chorus; many standards use a 32-bar AABA form, so each chorus of a solo covers those 32 bars.
Knowing the head lets listeners follow a performance: during the solos the melody disappears, but its harmony and length keep going in the background. Jazz lo-fi rarely follows this full structure, yet many tracks borrow the idea in miniature, introducing a short melodic theme, letting it drop out over the loop and bringing it back near the end.