The Best Efficiency Point (BEP) is the point H(Q), where a centrifugal pump operates at maximum efficiency.

It is determined by the Flow Rate and the Total Head at the respective pump speed.

Pump duty curves (and thus the BEP) are subject to shift from its water-specific curves when handling highly viscous fluids.

Also see:
Duty Point
Flow
Pump H-Q Curve
Total Head