The key is the handle that you assign to an object that allows you retrieve it later. A key is a sequence of Unicode characters whose UTF-8 encoding is at most 1024 bytes long. Each object in a bucket must have a unique key.
Keys can be listed by prefix. By choosing a common prefix for the names of related keys and marking these keys with a special character that delimits hierarchy, you can use the list operation to select and browse keys hierarchically. This is similar to how files are stored in directories within a file system. For more information, see Listing Keys.
Keys often have a suffix that describes the type of data in the object. For example, ".jpg" indicates that an object is an image. Although Amazon S3 supports key suffixes, they are not required.