The controls are discretionary in the sense that a subject with a certain access permission is capable of passing that permission (perhaps indirectly) on to any other subject (unless restrained by mandatory access control).
On the other hand, systems can implement both MAC and DAC simultaneously, where DAC refers to one category of access controls that subjects can transfer among each other, and MAC refers to a second category of access controls that imposes constraints upon the first.
[2] The term DAC is commonly used in contexts that assume that every object has an owner that controls the permissions to access the object, probably because many systems do implement DAC using the concept of an owner.
Users (owners) have under this DAC implementation the ability to make policy decisions and/or assign security attributes.
A straightforward example is the Unix file mode which represent write, read, and execute in each of the 3 bits for each of User, Group and Others.