Its interesting, there is the Continuum plane used to talk with past Avatars and also the Cosmic plane (for a lack of Canon term) to access cosmic energy and/or the avatarspirit/Raava. Cosmic plane also seem to be used to clear chakras. Korra used it without Raava to energy bend
Avatar Lore Update⚡
The spiral astral plane that avatars can contact past Avatars is called The Continuum. There is a clear difference between a spirit in the spirit world that anyone can interact with and a past avatar that only an Avatar can access in their mind.