Bottleneck

A bottleneck is literally the neck of a glass or pottery bottle.

Metaphorically a bottleneck is a section of a route with a carrying capacity substantially below that characterising other sections of the same route.

More generally, a bottleneck is one process in a chain of processes, such that its limited capacity reduces the capacity of the whole chain. A related concept is critical path (in Project Management) and the Theory of Constraints (as in Industrial Engineering and Operations management).