The word tack has several meanings:

1. A small, sharp nail with a flat, wide head used for attaching paper or fabric to walls or boards. Teachers use thumbtacks to pin student artwork on bulletin boards. Tacks are designed to push in easily with your thumb and pull out without much damage to the wall.
2. In sailing, to tack means to change direction by turning the boat's bow through the wind so the sails shift to the other side. Sailors tack back and forth in a zigzag pattern when they need to sail toward where the wind is coming from. Without tacking, a sailboat could only go in the direction the wind pushes it.
3. A course of action or approach to solving a problem. If your first strategy isn't working, you might try a different tack. When a teacher explains a math concept one way and students seem confused, she might take a new tack and try a different explanation.
4. The equipment used for riding horses, including saddles, bridles, and reins. A stable's tack room is where riders store and maintain their gear.