What is a bond beam?
Properly built concrete pools have a continuous bond beam around the entire perimeter of the pool.
A bond beam is the reinforced top portion of a pool wall, which is continuous around the perimeter to give the pool shell strength against various forces of pressure that might otherwise break the shell.
Think of a metal mixing bowl, or salad bowl. It's sturdy and does not easily bend, thanks to the reinforced strength of the rim around the perimeter. If you were to cut off that rim, the bowl would more easily bend or break.
A bond beam on a concrete pool is a continuous belt of reinforced concrete within the top of the wall. There is more rebar and thicker concrete within the bond beam compared to the rest of the wall.