Plain English Meaning
It is the small arrow with a barb printed on the approach chart that tells you which side of the inbound course to fly your course-reversal turn on.
Full Definition
The symbol on an instrument approach chart, shaped like an arrow with a barb, that indicates the direction (left or right) in which the procedure turn must be flown to reverse course and align with the final approach course.
Context Anchor
Seen on instrument approach charts when a published procedure turn is used to reverse course before continuing inbound.
Derivation
A 'barb' is the angled, hook-like point on an arrow or fishhook. The chart symbol is drawn with that same hooked shape, so chart designers called it a 'barbed arrow.' The barb points to the side of the inbound course where the turn must be flown.