A grouphead is a fixed component of an espresso machine. It is the receiver for the removable portafilter

Portafilter

A portafilter attaches to the group head of semi-automatic and piston-driven espresso machines, and carries a tamped puck of coffee grounds within its basket. It is usually made of brass, and is attached by a plastic or wooden handle...

 (or group handle). A typical consumer espresso machine

Espresso machine

An espresso machine is used to produce the traditional Italian coffee beverage called espresso.-History:The first machine for making espresso was built and patented by Angelo Moriondo of Turin, Italy, who demonstrated a working example at the Turin General Exposition of 1884. He was granted patent no...

 normally has only one grouphead, while popular professional machines, such as those used at commercial coffee shops, can contain anywhere from one to seven.

During the process of extracting a shot of espresso

Espresso

Espresso is a concentrated beverage brewed by forcing a small amount of nearly boiling water under pressure through finely ground coffee. Espresso is widely known throughout the world....

, hot water is forced through the grouphead under pressure. The grouphead contains many holes that attempt to distribute the pressurised water evenly over the surface of the grinds in the portafilter

Portafilter

A portafilter attaches to the group head of semi-automatic and piston-driven espresso machines, and carries a tamped puck of coffee grounds within its basket. It is usually made of brass, and is attached by a plastic or wooden handle...

basket and thereby achieve an even cross sectional flow.