Explanation: Access Control List is the document that defines who can access a particular bucket or object in Amazon S3. Amazon S3 Access Control Lists (ACLs) enable you to manage access to buckets and objects. Each bucket and object has an ACL attached to it as a subresource. It defines which AWS accounts or groups are granted access and the type of access. Reference:
http://docs.aws.amazon.com/AmazonS3/latest/dev/acl-overview.html