1. n. [Drilling]
The set of valves, spools, and fittings connected to the top of a well to direct and control the flow of formation fluids from the well.
See: cellar, formation fluid, shut-in bottomhole pressure, shut-in pressure
2. n. [Well Completions]
An assembly of valves, spools, pressure gauges and chokes fitted to the wellhead of a completed well to control production. Christmas trees are available in a wide range of sizes and configurations, such as low- or high-pressure capacity and single- or multiple-completion capacity.
See: choke, frac stack, frac tree, pressure gauge, production tree