The concept (known as duoteism) is mostly prevalent in Wicca, however different paths have different approaches. In general, most neopagan practices (like older polytheism e.g. Ancient Greece) are orthopractic (meaning practice takes precedence over belief).
This means that there are many ways to consider the Lord and Lady. Some see them as two balancing creative forces of the universe, others as actual spirits to be called upon and worshipped. Some give them specific names from various pantheons, while other simply call them God and Goddess.
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