Process tolerance is a value that sets the standard by which the capability of your process is determined. It is defined as a multiple of a process standard deviation (sigma). Usually, 6*sigma is used as a tolerance.
Some processes require a higher, stricter tolerance than others. For example, passenger safety depends on the components of an airplane. Therefore, the process that produces these parts must have a high tolerance. But if your process does not affect the safety of people and resources, a lower tolerance is permissible. For example, the manager of a company that makes feed for livestock may set a lenient tolerance on the length of food pellets because no serious consequences exist if they are misshapen, and it will waste company resources to hold the dimensions of livestock feed to the same tolerance as airplane parts.
Minitab uses the tolerance to calculate capability indices such as the Cp index, which compares the tolerance to the specification spread. If the tolerance range is greater than the specification spread, then your process needs improvement.
The bounds of the tolerance range are called tolerance limits.