Definition
A pipe or chamber with multiple openings that collects fluid or gas from several sources into a single passage, or distributes it from a single source to several outlets. In piston aircraft engines, the intake manifold distributes the fuel-air mixture from the carburetor or fuel injection system to each cylinder, and the exhaust manifold collects burned gases from each cylinder and routes them out through the exhaust system.
Plain English
A branched pipe that either splits one flow into several, or combines several flows into one. On an engine, it's the network of tubes that feeds the cylinders or carries away their exhaust.
Context Anchor
Seen in piston-engine aircraft systems, especially in discussions of intake systems, exhaust systems, and manifold pressure.
Derivation
From the Old English manigfeald, meaning 'many times' or 'having many parts.' The plumbing sense -- a single pipe with many branches -- carried this idea of 'one thing, many connections' directly into engineering.
Why Pilots Care
Manifolds control even distribution of mixture and exhaust flow; damage or blockage reduces power and can create hazardous conditions.
Intuition Check
Do not think of “manifold” as the pressure gauge itself. The manifold is the branched passage; manifold pressure is the pressure measured inside the intake manifold.
Example Sentence 1
The mechanic found a small crack in the exhaust manifold during the annual inspection.
Example Sentence 2
A leak in the exhaust manifold can cause loss of power and unusual noise during flight.