In the context of physics and mechanics, the "mean position" refers to the equilibrium or resting position of an oscillating or vibrating system. It is the central or average position around which a system oscillates or vibrates.

When an object or system undergoes oscillatory motion, it moves back and forth around its mean position. For example, in simple harmonic motion, a mass attached to a spring oscillates around its equilibrium or mean position, which is the position where the spring is neither stretched nor compressed.

In the case of a pendulum, the mean position is the position where the pendulum hangs vertically downward with no angular displacement. When displaced from the mean position, the pendulum oscillates back and forth due to the force of gravity.