A term used to describe applications that are critical to the survival of an enterprise. Mission-critical services require a combination of several factors, such as availability, reliability, serviceability and performance. Each of these must be weighted in importance to fit the particular mission to be supported.

Usually any application that is critical to the proper running of a business or activity. If this application fails for any length of time, you may be out of business. For example, an order-entry system may be considered mission critical if your business relies on taking lots of orders.

Being essential to the running of a business. Mission-critical tasks must be conducted on a 24x7 basis.