What are Access Control Lists?

An access control list (ACL), is a list of permissions attached to an object.

An access control list (ACL) is a list of access controlentries (ACE). Each ACE in an ACL identifies a trustee and specifies the accessrights allowed, denied, or audited for that trustee

any real world thing is called object. allocation , assignmnt of object resources is called access control list. accounting information maintain in ACL  

It helps you manage and control user access based on the assigned role. 

An access control list (ACL), with respect to a computer file system, is a list of permissions attached to an object. An ACL specifies which users or system processes are granted access to objects, as well as what operations are allowed on given objects.