General Purpose:

Windows : The access control list (ACL) is a list of permissions in an operation associated with an object. Each of these permission entries is know as Access Control Entry (ACE). In general, an ACE contains permissions associated with a particular object (Like File/Folder) for a particular identity ( for an user or a group of user) . For example, for file system objects, you can set ACLs (read/write/execute operation) on files/directories on an NTFS file system.