Industry Standard Definitions - On Availablity

High Availability (HA)– 

     The attribute of a system to provide service during defined periods, at acceptable or agreed upon levels and masks UNPLANNED OUTAGES from end-users. It employs Fault Tolerance; Automated Failure Detection, Recovery, Bypass Reconfiguration, Testing, Problem and Change Management

Continuous Operations (CO)- 

     Attribute of a system to continuously operate and mask PLANNED OUTAGES from end-users.  It employs Non-disruptive hardware and software changes, non-disruptive configuration, software coexistence .

Continuous Availability (CA)- 

     Attribute of a system to deliver non disruptive service to the end user 7 days a week, 24 HOURS A DAY (there are no planned or unplanned outages). It includes the ability to recover from a site disaster by switching computing to a second site.