it means : 1 – Facing the direction of the Ka’bah 1- When you stand up to pray, face the direction of the Ka’bah wherever you are, in both fard (obligatory) and naafil (supererogatory) prayers. This is one of the pillars of prayer, without which prayer is not valid. 2- The obligation of facing the direction of prayer does not apply to one who is engaged in warfare, when he prays the fear prayer (salaat al-khawf) or is engaged in heavy fighting. It also does not apply to those who are unable to do it, such as one who is sick, or one who is traveling on a ship, in a car or on a plane, if they fear that the time of the prayer will elapse (before they reach a place where they can find the correct direction). And it does not apply to one who is praying a naafil prayer or witr prayer whilst riding on a riding-animal etc., but it is mustahabb for him to face the qiblah if he is able to do so when pronouncing the takbeer of ihraam (at the beginning of the prayer), then he may face whatever direction he is facing. 3- Everyone who can see the Ka’bah must face it; those who cannot see it must face its direction. http://islamqa.info/en/ref/13340