Amazon S3 is designed to store objects. Objects are stored in buckets and consist of a value, a key, metadata, and an access control policy.
The object value is the content that you are storing. The object value can be any sequence of bytes, but must be smaller than five gigabytes. There is no fixed limit to the number of objects you can store in Amazon S3.
The key is the handle that you assign to an object that allows you retrieve it later.
Metadata is a set of key-value pairs with which you can store information regarding the object.
The access control policy controls access to the object.