"High pressure pump" means that the cylinder wall, piston, etc. can withstand greater pressure and can inject high pressure into the inflated object.
The gas cylinder consists of a piston rod and a valve. The function of the valve is to allow only air to enter the inflated object from the pump, and does not allow air to return to the pump from the inflated object. The bottom of the piston rod of the pump is a raised rubber bowl. Pull the piston rod up and the air enters from around the cup. When the piston rod is pressed down, the air is compressed, and the increase of the pressure causes the rubber bowl to closely adhere to the wall of the air cylinder so that the air cannot leak, so the air is driven into the inflated object.