DAC = Discretionary Access Control
MAC = Mandatory Access Control
ACL = Access Control List
The ACL specifies the controls to be applied by the method of control, DAC or MAC. MAC is explicit, centrally controlled, and does not allow users to grant authority to an object unless they have explicit permissions to do so, whereas DAC allows users to grant other users access to objects they can access.
MAC ACLs will always be applied to a request first, and if access is denied processing stops. If access is permitted then the DAC ACLs are applied, and again if access is denied processing stops. Only if access is granted by both MAC and DAC ACLs can the user access the object they requested.
SELinux is a MAC implementation for Linux (there are others), while the traditional
rwx file permissions, combined with the owning user and group form the complete DAC ACL. The SELinux 'policy' is essentially the MAC ACL.
setfacl extends the basic filesystem ACLs to allow more than a single user or group to be assigned an to ACL for files and directories. This is also a DAC implementation, and is therefore applied after the SELinux MAC ACLs.