ITIL definitions describe three types of change:
Major
Standard / Normal
Urgent / Emergency
Standard and normal changes are usually counted as two separate types. A standard change is routine, not a large upheaval, and can be implemented within the Service Desk team. A normal change is larger and will involve members of other departments. A major change is a big undertaking that will create a new service or radically alter existing IT infrastructure. An urgent change is usually in response to s sudden system failure that needs to be corrected to keep the business operating.