olemus
ITIL:
äriprotsessi osa, mis on ettevõttele elutähtis; elutähtsad äriprotsessid on olulised tegurid jätkusuutlikkuse halduses, IT teenuste jätkuvuse halduses ja käideldavuse halduses.
= part of a business process that is critical to the success of the business Vital business functions are
an important consideration of business continuity management, IT service continuity management and availability management.

ülevaateid
http://www.itsmsolutions.com/newsletters/DITYvol5iss50.htm
https://www.edupristine.com/blog/the-different-business-functions-by-edupristine/
https://cio-wiki.org/wiki/Vital_Business_Function_%28VBF%29#google_vignette