Note also some others will replace "beam reach" with just "reach."
Take special note of HPLou's reference to "apparent wind." Apparent wind can make or break a sailor. Knowing true wind direction, and apparent wind direction (which is the direction wind "appears" to come from due to your own velocity moving forward), can help you determine the "best line to a mark."
In light wind any forward momentum you have while entering a wind shadow can cause you to chase your windex around a circle. Also using ApWind technique you can keep your sails filled and "point higher" while coasting through a wind shadow. All depends on that Apparent Wind direction.