Amazon Simple Storage Services is object storage allowing customers to put data in the cloud with 99.99999999999% availability. S3 should not be confused as a file system, as it is not designed for that purpose. Object storage typically includes the data itself, a variable amount of metadata, and a unique identifier that allows applications to read it. Companies with very large data sets can also store data cost effectively by utilizing different S3 storage classes that are priced at different tiers. Data that is accessed frequently costs more, while data that is not accessed often is cheaper. This allows for flexibility when designing data architectures. S3 also includes very granular security permissions to be able to determine who can access data. This is a very important part of the public cloud and being able to secure applications that can read data can minimize data breaches and leaks.
in other words
Amazon's version of Dropbox or Google Drive, for businesses.