Definition - What does Wellhead mean?
A wellhead is the equipment that acts as the surface termination point of an oil or gas well. During construction, the wellhead provides the support for casing hangers. During production, the wellhead houses the Christmas tree, which consists of valves and piping to control the pressure of the well during production.
Trenchlesspedia explains Wellhead
Two critical aspects of wellhead design is the ability of the wellhead to provide a pressure seal under production conditions and the ability of the wellhead to handle the mechanical loading of the drill string. A blowout preventer is attached to the wellhead during drilling to prevent a pressure rupture of the well by completely enclosing the casing. A Christmas tree is attached to the wellhead during production to control flow and pressure and to provide the connectivity to the production processing facility.