It refers to any world or galaxy which exists in this universe. It can be visible and physical, like our world and everything in it, or invisible to mankind. According to Islamic traditions, Aalam Al-Arwah is the realm where souls exist before they come to this world, Aalam Al-Dunya is this material world while Aalam ul Akhira is the hereafter. The world which exists between Aalam Al-Dunya and Aalam Al-Aakhira is called Aalam e Barzakh and it is this realm where the souls go when they depart the body.