Many pagans worship nature, but there are nature-worshippers who don’t call themselves pagans, like the naturalistic pantheists. Many pagans believe in a multitude of Gods and Goddesses, polytheism, but there are some polytheists who aren’t pagans, like the Mormons (a Christian sect). Some who call themselves pagans are neither nature-worshippers nor polytheists, but their paganism consists in working magic, like the Thelemites. There is no easy way of classification. I would say all practitioners of Wicca, Hellenismos, Ásatrú, Religio Romana, Kemeticism, Neocelticism, Druidism, Romuva, Hinduism, Native American religion and African religion (and this is just a partial list) are pagans. Jews, Christians and Muslims certainly aren’t. Buddhists aren’t either. Taoists may qualify, if their belief in Gods has any impact. Shintoists perhaps also. Atheists can be pagans if they revere nature and call themselves pagans.