When creating a process definition, select Add DefinitionCriteria to add one or more criteria to act as condition(s) for when the process should run. (For example, run only if an account’s industry is "Manufacturing".) When all rules are met, the process executes. Criteria are used to further refine when a definition is used. Along with the object name and its record type, each condition must be met for a process to kick off using this definition.