Throughput = units of finished goods produced per unit of time, usually per hour, shift, day or week. Only completed, saleable units count; work-in-progress does not. The distinction matters because it prevents inflating throughput by pushing more inventory into the system instead of actually delivering more product.
A factory can produce a lot of output that doesn't count as throughput: units still in WIP, units awaiting inspection, units in finished-goods inventory beyond real demand. Throughput measures only what actually leaves the factory as saleable product. This is the number that turns into revenue; everything else is either potential or waste.
System throughput equals the throughput of the bottleneck. Investments to increase throughput anywhere else are wasted; investments at the bottleneck raise the ceiling for the whole system. This is why the Theory of Constraints puts so much emphasis on identifying and elevating the bottleneck, it is the single point that determines the total.
Throughput is the honest measure of production. It tracks what customers actually receive, not what the factory has been busy doing. Combined with lead time and flow efficiency, it produces a picture of how well the system is serving its purpose.
