# lineItem/AvailabilityZone #level100 #cur #finops #curfield Availability zone (AZ) identify the sub-location (sub-region) in which the instance of system is running Availability zones are defined with the name of the main region followed by a letter. - a for the first availability zone - b for the second one - and so on For example, `us-east-1a` or `us-east-1b` as AZ of the us-east-1 region. ## Source - Category: [[Line item details]] - [AWS documentation](https://docs.aws.amazon.com/cur/latest/userguide/Lineitem-columns.html) ## Relevant notes ## Notes In each AWS region is really a network of different datacentres tightly connected together. Each individual datacentre is an Availability Zone. For [[300 - disaster recovery]] purposes, each availability zone should be able to survive a catastrophic event without impacting the other availability zone in the same region. So if you save some data in the London region, for backup and fault-tolerance, that data will be saved into an availability zone of the London region and replicated in at least another availability zone of the London region.