Q* is the optimal (ie, correct for the decision problem) function computing the total expected reward of taking an action from a given state in reinforcement learning.
The "star" in A* means optimal (as in actually proven to be optimal, so they could stop publishing A^[whatever] algorithms). I assume either Q* is considered optimal in a way regular Q-learning isn't, or they're mixing Q-learning with some A*-like search algorithm. (Or someone picked an undeserving name.)
