ACLs, pronounced “ackkls,” can provide greater control over file permissions. You add ACLs when traditional UNIX file protections are not sufficient. Traditional UNIX file protections provide read, write, and execute permissions for the three user classes: owner, group, and other. An ACL provides finer-grained file security.
ACLs enable you to define the following file permissions:
Owner file permissions
File permissions for the owner's group
File permissions for other users who are outside the owner's group
File permissions for specific users
File permissions for specific groups
Default permissions for each of the previous categories
For more information about using ACLs, see Using Access Control Lists to Protect Files.