To me, tactics encompasses things like where to hit the ball and when, court positioning, and shot selection. Anything you can draw on a chalkboard with arrows and such would be tactical. It is one level below Strategy which is a higher-up thought process.
Tactics is all about knowing what is a high percentage shot (easy to make) and what is a low percentage shot (hard to do). If you know what shots can be made from where in the court, you not only can select what you should do, but you also know what your opponent has to do. You start thinking 2-3 moves ahead like in chess.
LEVEL UP!!!! Now that you are thinking tactically about each point, learn about Match Strategy!