What does High Availability actually mean?

Traditionally, it was just making all the resources available especially the data through redundant components but the terminology has changed now.

High availability can now be defined through various terms –

.  High-end online availability of resources
.  Non-disruptive upgrades, reconfigurations and serviceability
.  Predictable performance
.  Great application response
.  Scalable architecture
.  Flexible and supports multiple protocols
.  Easy to manage