Alaya (Sk. अलय). The Universal Soul (See Secret Doctrine Vol. I. pp. 47 et seq.). The name belongs to the Tibetan system of the contemplative Mahâyâna (Sk. महायान) School. Identical with Âkâsa (Sk. आकाश) in its mystic sense, and with Mulâprâkriti (Sk. मूलप्रकृति), in its essence, as it is the basis or root of all things.
Source: H.P.Blavatsky - The Theosophical Glossary