A manifold is a wide and/or bigger pipe, or channel, into which smaller pipes or channels lead.
An inlet manifold or intake manifold is the part of an engine that supplies the fuel/air mixture to the cylinders.
In contrast, an exhaust manifold collects the exhaust gases from multiple cylinders into a smaller number of pipes – often down to one pipe.
The primary function of the intake manifold is to evenly distribute the combustion mixture (or just air in a direct injection engine) to each intake port in the cylinder head(s). Even distribution is important to optimize the efficiency and performance of the engine. It may also serve as a mount for the carburetor, throttle body, fuel injectors and other components of the engine.