Note: This term may have other meanings in other contexts. Here, we are defining it in the context of a distributed database.
High Availability is a desirable characteristic for databases; it describes the ability of a database to survive (and thus remain available) even when parts of the system fail. For example, a CockroachDB database with five nodes could survive and remain available even if several nodes failed.
Different databases use different models to achieve high availability. The two most common high availability models are Active-Passive and Active-Active. Meanwhile, CockroachDB uses a Multi-Active Availability model.