As Defined In The Dictionary: A condition in which all physical influences are canceled by others, resulting in a stable and neutral system.

As Defined In Physics: The state of a body at rest or in constant and unchanging motion.

As Defined In General Physics: The condition of a system that has its total energy distributed among its component parts in the statistically most balanced manner.

As Defined By BioPosture: To "Sleep In Natural Balance" for the ideal combination of support and comfort! The significance of sleeping on your mattress, not, in it... To enjoy the feeling of buoyancy.