Self-priming pump
Also called: self priming pump, non-self-priming pump, pump priming.
A self-priming pump can pull water up to itself, so it can sit above the pool's water line. Pumps designed for in-ground pools are self-priming. Most above-ground pumps are not: they sit on the ground below the water line and gravity fills them before they run.
Why it matters
The difference decides where a pump can sit and how you troubleshoot it. Hayward says its PowerFlo LX and PowerFlo VS 300 must be installed below the pool water line; only its self-priming PowerFlo II may sit up to four feet above it. Pentair says its Dynamo will not lift more than 8 feet. So an above-ground pump that runs but moves no water is almost always starved, not broken. Turn it off first, because running dry damages the seal. Even a self-priming pump cannot prime instantly when dry: fill the pump basket with a hose and seal the lid o-ring with silicone lubricant.
In numbers
Hayward's manual for a pump with a strainer pot: fill the pot with water before starting, and if the pump has not primed within ten minutes, stop the motor and find the cause.