Meaning of Circulating pump Delivery Head

Hi could someone please, tell me the meaning of maximum delivery head on a circulating pump.

thanks

The simplest way to answer this is that the Head pressure is the maximum resistance to flow the pump can over come, or if it was pumping straight up it would be the height that the pump would stall and not push the liquid up.

Imagine an arrangement of a loop of pipe with a pump at the bottom and the pipe coming out went up to a tank, where it drained openly and a overflow ran the liquid back down to the pump to go around again. The difference in height from the pump to the out flow is the head - usually given in feet or inches (or meters) and with most pumps the greater the head, the lower the flow or the greater load on the motor until it stalls, which is the maximum.
In practice, each elbow and reduction coupler or valve also acts as if there were a "head" and so the pump might not deliver even though the height from pump to output is less than the specification

It's an centrfiugal impeller pump right?
Above a certain 'head' pressure, the impeller 'stalls' and you get no flow.