(Sanskrit) Literally, "fundamental quality."
"Prakriti is composed of the three Gunas or forces, namely, Sattva, Rajas and Tamas. Sattva is harmony or light or wisdom or equilibrium or goodness. Rajas is passion or motion or activity. Tamas is inertia or inaction or darkness. During Cosmic Pralaya these three Gunas exist in a state of equilibrium. During Srishti or projection a vibration arises and the three qualities are manifested in the physical universe." - Swami Sivananda, Kundalini Yoga
"Sattva, Rajas and Tamas (harmony, emotion and inertness) were in a perfect, nirvanic equilibrium before the dawning of the dawn of the Mahamanvantara. The fire put the cosmic scale in motion. Sattva, Rajas and Tamas were unbalanced; therefore, the Mahamanvantara dawned. The yogi must liberate himself from Sattva, Rajas and Tamas to gain the right to enter into the Absolute. Sattva, Rajas and Tamas will be in perfect equilibrium again at the end of the Mahamanvantara; thus, the universe will sleep again within the profound bosom of the Absolute, within the supreme Parabrahman, the In-nominated." - Samael Aun Weor, Kundalini Yoga: The Mysteries of the Fire