The average rate at which (non-defective) finished product exits a process. In a line consisting of successive workstations dedicated to a single family of products and where all products pass through each station only once, the throughput of each workstation is the same. When workstations handle multiple routings the throughput of an individual workstation will be the sum of the throughputs for each of the different routings passing through it.
Theory of Constraints states that process throughput is limited by the throughput of the process constraint. It can be increased only by increasing throughput at the constraint.
Capacity is the upper limit of a process' throughput.