What are world religions?

World religions are religions with many followers that have crossed national borders. Examples of world religions are Christianity, Islam, Hinduism and Buddhism. These are the top four major religions in the world as ranked by the number of adherents. Christianity leads with 2.1 billion followers, followed by Islam (1.3 billion), Hinduism (900 million) and Buddhism (376 million). These religions have spread to most parts of the world.