Definition: A virtual or physical representation of having accomplished something. These are often viewed as rewards in and of themselves.
Example: a badge, a level, a reward, points, really anything defined as a reward can be a reward.
2. Appointment Dynamic
Definition: A dynamic in which to succeed, one must return at a predefined time to take some action. Appointment dynamics are often deeply related to interval based reward schedules or avoidance dyanmics.