The literal definition of constraint is that it is a limitation or a restriction. To better explain constraint in the context of TOC (deriving from an example of the Theory of Constraints Institute), imagine a chain and its weakest link. By identifying which is the chain’s weakest link and strengthening only that one link, you will be able to increase the strength of the whole chain.
In a business process or a manufacturing assembly line, identifying what is the weakest link (constraint) and focusing on improving it will help elevate the overall performance of the business and increase its throughput.