Final answer:
High Availability, as defined by Palo Alto Networks, refers to the continuous operational performance of systems with minimal downtime through redundancy and failover mechanisms.
Step-by-step explanation:
The definition of High Availability according to Palo Alto Networks, a leading cyber security company, generally refers to the ability of a system or infrastructure to remain operational and accessible, without significant downtime, even in the event of failures or maintenance. High Availability systems are designed to ensure an agreed-upon level of operational performance for a higher than normal period. In the context of Palo Alto, this often means redundant systems, failover mechanisms, and well-planned disaster recovery strategies to ensure network security appliances and services are always running to protect against cyber threats.