Plain English Meaning
A set of circles, one inside the other, sharing the same center point. On an approach chart they show how far you are from a key point on the ground.
Full Definition
On an instrument approach chart plan view, concentric rings are evenly spaced circles drawn around a central reference point (typically a navaid or airport) used to indicate distance from that point. They appear inside the Minimum Safe Altitude (MSA) circle and help the pilot quickly judge range from the reference fix.