Anything that limits production. These can be physical – a bottleneck – or managerial. Managerial constraints may be due to market demand or company policy (e.g. limitations placed on daily hours worked), and come into play once the series of physical bottlenecks is identified and eliminated.
Constraints can be used to manage throughput. In a well-balanced cell, bottleneck operations can be activated or deactivated according to demand. Kanbans and supermarkets can be used to link cells so that the entire process can be managed by managing one constraint.