Definitions for "High availability"
Systems or applications requiring a very high level of reliability and availability. High availability systems typically operate 24x7 and usually require built-in redundancy to minimize the risk of downtime due to hardware and/or telecommunication failures.
A configuration that enables two Solaris servers to run a single instance of Calendar Server 5.1 that remains continuously available after any single point of failure in hardware (disk, server, or network) or software has occurred in either of the servers.
The ability of a system or network to be accessible almost all of the time, through additive or built-in mechanisms that make the resource tolerant of failures. The most common implementation to achieve high availability is to provide a hot failure-over mechanism. This ensures that, in the case of failure, a standby system would take over operation. When talking about high availability systems, the measurement of the capabilities is the switch-over time, and whether or not any information/connection is lost during the switch-over. High availability can be achieved using software and/or hardware.
The ability to keep an application or service operational and usable by clients most of the time.
(Real Application Clusters Administration; search in this book) [definition #2] (Real Application Clusters Concepts; search in this book)
Keywords:  assembler, level