High availability is a term used to describe a system or a service which is ready to be used, therefore “available”, almost all the time. Availability refers to the situation when a user has access to and can use the resources of a system, service or a device, either to work, add new elements or use the databases. If user cannot do any of those, it is said they are unavailable.
higher availability than the more complex ones. This is because there are more elements that are threatened by potential failures.