Legendarium is the term Tolkien used for his written works about the mythology of Eä.
Letter 131: "This legendarium ends with a vision of the end of the world..."
Letter 153: "...my legendarium, especially the 'Downfall of Númenor' which lies immediately behind The Lord of the Rings, is based on my view..."
Letter 154: "Actually in the imagination of this story we are now living on a physically round Earth. But the whole 'legendarium' contains a transition from a flat world..."
Letter 163: "But the beginning of the legendarium, of which the Trilogy is part (the conclusion), was an attempt to reorganise some of the Kalevala ...."