Scootertrash From United States of America, joined Aug 2001, 569 posts, RR: 10 Reply 1, posted (10 years 1 month 4 weeks 1 day 10 hours ago) and read 2297 times:
What you are referring to is air that is taken from the compressor section of a turbine engine for uses other than engine operation. This is referred to as "bleed air." Bleed Air is used for lots of stuff: Running the air conditioning and pressurization, starting the opposite engine (sometimes), pressurizing door seals (on some airplanes), powering deicing/anti-icing equipment... The list goes on.