Taken from (TOC) “Theory of Constraints” A constraint is anything that limits a system from achieving higher performance relative to its’ goal.
Comments: In practical application a “Company’s Constraint” is the biggest limiting factor that reduces the amount of throughput the company can achieve. This may mean a machine or process that is the slowest operation (bar none). A company can have many bottlenecks, but in order to be the Constraint of the company it must be the “Alpha Bottleneck” that effects the throughput of the company as a whole.
Some companies have more than one Constraint. Although one may be slightly larger than another, working to “break” 2 or 3 constraints of approximately the same size or limiting nature simultaneously is a worthwhile pursuit.