When talking about the cloud, it is important to understand how the infrastructure is managed. Three basic concepts
Region: A Region is a separate geography unit where the cloud has a presence in terms of infrastructure.
Availability Zone: Within a region, a cloud has multiple availability zones, to handle local failures.
Data Center: Within an availability zone, the cloud can have multiple data centers. It can simply be a building where infrastructure is managed for a cloud.
Understanding this concept is important to manage disaster recovery scenarios and making sure available. For example, when you are storing data, you will be asked what kind of replication strategy you need. A Local replication would mean that data is replicated within the datacenter, so in case of disk failure, your data is safe and available. Whereas in the case of zone replicated data, it would mean that data is copied across the zones and can handle a data center failure. Finally, a region or cross-geo replication makes sure that data is replicated across regions, making sure you never lose your data even if a whole region is down. Each strategy has a cost impact, so based on the criticality of data one needs to choose the strategy that fits best.