A Discipline is a business rule. You can prevent unauthorised Users from performing certain functions that could adversely affect the outcome of business transactions. These rules are called Production Rights.
For example, Chase has a Production Right that restricts certain Users from ordering above what has been estimated on a CE. A discipline can be created to make an exception for Users who have no rights to perform this type of transaction. This exception is called an override, and may only take place through an appropriate approval process.