Wind or current pushing your boat off course causes leeway. Boats with a large amount of surface area above the waterline (freeboard) will be affected by the wind to a greater degree than low-profile boats. Boats with a large keel or underwater profile will be affected by current to a greater degree than planing boats with less structure under the water. You should compensate for leeway by steering into wind or current in order to make good a straight course to your destination.
You can visualize leeway by looking back at your wake while on a steady compass heading. If your wake is not following directly behind you, but being set to one side or the other, you are experiencing leeway and should correct your course.