Amazon Elastic Compute Cloud (EC2) is a web service that provides scalable computing capacity in the cloud. EC2 is designed to be highly available, fault-tolerant, and scalable, and it achieves these goals through the use of regions and availability zones.

An Amazon EC2 region is a geographic location where Amazon has multiple data centers that are interconnected through a low-latency network. Each region is completely independent of the other regions and is designed to provide high availability and fault tolerance. AWS currently has 25 regions worldwide, each with its own set of availability zones.

An Amazon EC2 availability zone is a distinct location within a region that is engineered to be isolated from failures in other availability zones. Availability zones are connected to each other through high-speed, low-latency networks, allowing applications to run across multiple availability zones for increased availability and fault tolerance. Each availability zone consists of one or more data centers, each with its own power, networking, and connectivity, to provide redundancy and isolation.

By launching instances in multiple availability zones within a region, users can ensure that their applications remain highly available even in the face of component failures or network outages. Users can also use multiple regions to achieve geographic redundancy and ensure that their applications remain available even in the face of regional disruptions.