A penis pump is an apparatus used to stimulate the penis into an erection, generally for the purpose of sexual intercourse where penetration is desired.
A penis pump operates in the same way as a vacuum. A penis owner inserts their penis into the tube of the pump and then uses a pump attached to the tube to pump air out of the tube. This applies suction to the penis, drawing blood inside.
Many penis pumps also include a cock ring that is used to keep the blood inside the penis, resulting in an erection.
Recreational penis pumps can often be obtained as bedroom accessories while medical grade pumps used to aid in the treatment of erectile dysfunction (the inability to achieve an erection for sufficient sexual interaction) can be purchased from medical supply venues. Some health insurance plans may cover the purchase of a medical-grade pump with a doctor's diagnosis.