Mission-Critical is a term that refers to something that is indispensable.
Mission-Critical is a term that refers to something that is indispensable. It usually describes applications such as databases or process control software that are deemed essential to a company's operation and that typically run on mainframes or workstation rather than on personal computers. e.g. A nuclear power plant's operator console software is mission critical.
Reference: www.netdictionary.com/m.html