The TOC Dictionary provides the following definitions:
The rate at which the system generates “goal units”.
Usage: Because throughput is a rate, it is always expressed as goal units per unit of time (e.g., hour, day, month or year) or unit of product. If the goal units are money, throughput will be an amount of money per time period or per unit of product. In the case of throughput per time period, throughput is calculated as (revenues received for the period minus totally variable costs) divided by the chosen time period. In the case of throughput per unit of product, throughput is calculated as the selling price of the product minus totally variable costs per unit.
Cox III, James F., Lynn H. Boyd, Timothy T. Sullivan, Richard A. Reid, and Brad Cartier, 2012, The Theory of Constraints International Certification Organization Dictionary, Second Edition, page 121.
The view that a system consists of a series of dependent variables that must work together to achieve the goal and whose ability to do so is limited by some system constraint. The unavoidable conclusion is that global improvement is the direct result of improvement at the constraint, and cost allocation is unnecessary and misleading. This paradigm is in conflict with the cost-world paradigm.
Cox III, James F., Lynn H. Boyd, Timothy T. Sullivan, Richard A. Reid, and Brad Cartier, 2012, The Theory of Constraints International Certification Organization Dictionary, Second Edition, page 123.