The pit can refer to the auxiliary percussion section of some high school or college-level marching bands.
The Pit vs. Band/Colorguard
The players in pit do not march.
They do not learn drill at band camp.
They do not play for six hours in the pouring rain.
This is because:
Grand marimbas are nearly impossible to march.
Drill is for those who can pick up their instruments.
Water can damage the chimes and xylophones.
(The band/colorguard only seem to notice that the pit doesn't march and therefore envy the pit players.)
Members of The Pit
In higher levels of marching bands, the pit can be an impressive ensemble of talented percussionists who have spent crazy hours practicing and mastering every instrument of the pit from the triangle to the bass drum to the vibraphones.
In many high school marching bands, the pit consists of a few percussionists as well as players of unmarchable instruments (bassoon, english horn, stringed instruments, etc.)