Bleed

Bleed is used to describe air extracted from the compressor stages of an engine for some purpose other than combustion with fuel. There are different types of bleed

Aircraft Bleed

Bleed air drawn off the engine compressor section to deliver to the aircraft, most commonly for supply to the aircraft environment control system for delivery to the passengers / cargo compartment. Also known as customer bleed by engine manufacturers.

Handling bleed

Bleed air drawn off the engines compressor stage(s) to avoid surge or stall of the airflow through the engine.

Engine cooling and sealing bleed

Generically part of the engine internal air system, taking air from the compressor (possibly at more than one point along it) and using the air for various purposes in the operation of the engine, most commonly component cooling in the hot parts of the combustion system and turbines, and for sealing airflows, e.g. into bearing chambers to prevent ingress of destructively hot air from the main gas path.