Availability is the property of ensuring that an asset can be used when it is needed. In other words, availability protects against the threat of denial of service. It is one of the three key security properties of an asset, along with confidentiality and integrity.
Availability is the property of an asset that states that it is always accessible when needed. In other words, it requires that attackers cannot prevent legitimate access by committing a denial-of-service. It is one of the three elements in the classic CIA triad of security properties, alongside confidentiality and integrity.