An act which proceeds directly from human reason and free will. An example of a good human act is the decision of an agent to be charitable to his neighbor. The agent knows charity is a good (reason) and chooses to do it (free will).
Conversely, a human act can be evil in nature by implementing the same principles of intellect and free will. An agent chooses to do harm to another (reason) and acts on the idea (free will).
In both good and evil human acts, the person is the master of his act.