Access list control

An access control list (ACL) is a table that tells a computer operating system which access rights each user has to a particular system object, such as a file directory or individual file. Each object has a security attribute that identifies its access control list. The list has an entry for each system user with access privileges. The most common privileges include the ability to read a file (or all the files in a directory), to write to the file or files, and to execute the file (if it is an executable file, or program).








Different Operating System (OS) may use different Access Control List. When a user wants to initiate a specific action against a component item (for example, edit an article), the system checks the permission for this combination of user, item, and action. If it is allowed, then the user can proceed. Otherwise, the action is not allowed.
Allow: Allows this action for this level and group and for lower levels and child groups. This does not have any effect if a higher group or level is set to Deny or Allow. If a higher group or level is set to Deny, then this permission will always be denied. If a higher group or level is set to Allow, then this permission will already be allowed.
Deny: Denies this action for this level and group.
Access control list may include networking Access Control List (ACL), filesystem ACL and etc.







Reference:
http://en.wikipedia.org/wiki/Access_control_list
http://searchsoftwarequality.techtarget.com/definition/access-control-list