Plain English Meaning
It is the side of the racetrack-shaped pattern where the airplane actually does its turning and outbound flying. The other side is just the straight inbound leg back to the fix.
Full Definition
The maneuvering side is the side of a holding pattern or course reversal where the aircraft turns and flies the procedural legs to reverse direction. On a published holding pattern, it is the side opposite the inbound holding course, where the outbound leg and the turns are flown.
Context Anchor
Seen on instrument approach charts and in course reversal discussions, especially with procedure turns and holding-pattern course reversals.
Derivation
comes from the French manoeuvre, meaning 'to by hand' or 'to handle.' The maneuvering side is simply the side where does the handling work — the turns and outbound flying — as to the inbound leg, which is mostly straight back to the fix.