The Theory of Constraints describes an alternative type of system to a Kanban System, or to an MRP system. The Theory of Constraints is based on the idea that any production system has one or more 'bottlenecks' that limit the output. Increasing the capacity of any work station, other than a bottleneck, serves no purpose.
TOC was developed by Eli Goldratt who wrote a book called 'The Goal' to illustrate its operation. He used the analogy of a group of schoolboys on a long and hard walk to an overnight camp. One fat child lagged behind and the others had to keep stopping whilst he caught up. Eventually the leader (the author) realized that sometimes the fat boy had to wait in a queue when the group had to negotiate a section that could only be taken one at a time. It was better to put the fat boy at the front where his progress was never impeded. They also inspected the fat boy's rucksack and found it overweight and full of unnecessary items that they either discarded or distributed to the fitter members. (hope I haven't spoiled the book for you)