Bottleneck
A bottleneck is the resource in a process whose limited capacity constrains the throughput of the whole system. Output can never exceed the bottleneck's capacity, so improving anything else yields no gain until the bottleneck is addressed.
Every process has a slowest step, and that step governs the rate of the entire flow. Effort spent speeding up non-bottleneck resources merely builds inventory in front of the constraint without raising true output. The theory of constraints formalises this: find the bottleneck, exploit it fully, subordinate everything else to it, then elevate its capacity — after which the bottleneck usually moves elsewhere and the cycle repeats.
Related terms
Theory of Constraints (TOC) · Value Stream Mapping (VSM) · Takt Time