H
high availability or highly available (HA)

(n.) A greater level of availability typically due to component redundancy. Typically, HA refers to a failover cluster environment in which a service is provided by a primary server until a failure causes that service to be failed over to a secondary server that then becomes the primary server.

horizontal scaling

(n.) Typified as achieving scaling and resilience through replication of a service component (for example, a web server or application server). For scaling to be effective, the workload, or data processed by the service component, should be partitionable. This contrasts with vertical scaling.

See also [vertical scaling]
HVAC

(abb.) Heating, ventilation, and air control

hypervisor

(n.) A virtual ...

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