Full form of S3 is Simple Storage Service

S3 is an AWS provided storage service platform for managing, storing and retrieving files and other static data/assets. S3 provides industry leading availability, performance, scalability, and security and can be used for various different use-cases e.g. to host a simple static websites or for managing user uploaded files.

S3 is relatively cheaper compared to other similar services and integrates well with all other AWS and non-AWS services (by using APIs). It offers integrated solutions for encryption, audit, compliance and security. S3 also has a number of storage classes that can be utilized for use-cases that need to store large amounts of infrequently accessed data (e.g. backups) at a lower price.