An Access Control List (ACL) is an access control mechanism in Amazon S3. It allows you to specify who can use Amazon S3 resources, such as a bucket or an individual file, and in what way. An ACL defines permissions – such as read or write access – assigned to specific AWS accounts or user groups.

It is mainly used for simple data sharing, for example, making files public or granting shared access to other accounts. While easy to configure, it offers limited flexibility and scalability. Therefore, in more complex environments, it is recommended to use Bucket Policies, IAM Policies, or Access Points, which allow for more precise and secure access management.