In November 2018 the Chinese eCommerce company Alibaba had generated over one billon Euros Sales at the shopping event Singles' Day - within the first two minutes only (sic!). This shopping event caused a massive peak in required data processing power. It is just one example of the importance of high availability of computational capacities and system stability for certain business models. Availability has a similar significance for Deutsche Börse, namely for its trading system.
The definition of high availability is simple (compare Wikipedia): a system is considered highly available if an application is still available even in the event of an error and can continue to be used without direct human intervention. Availability can be expressed as a percentage, namely as the ratio of (unplanned) downtime to the total production time of a system. We speak of high availability from 99.9% or more.
