exhaust pipe

Short definition from Wiktionary

Noun

1. 1
   For internal combustion engines, any of several pipes, connected in series, that carry waste gases away from the engine and vent it to the air.
2. 2
   For internal combustion engines, any of several pipes, connected in series, that carry waste gases away from the engine and vent it to the air: The final pipe in this series.
3. 3
   On a steam locomotive, a pipe which takes away steam exhausted from a cylinder.