In chess, tactics are the moves, or short combinations and chains of moves, you make as you play the game. The goal of tactics is to advance your own position while simultaneously reducing the number of options your opponent has.
This is a good tactics and strategy book. Not for the beginner but any club player would do themselves a favor by reviewing this book every other year or so along with some of the other 'required reading' of the chess classics.
Dr. Euwe was a psychologist and GM. If you can find an inexpensive copy of his classic book probing into the haunted-house of bobby fischer's head, that's a read that will stay with you for a long time. Euwe has plenty to say inside and outside the player's head.