Earnshaw's Theorem states that it is impossible to achieve stable equilibrium for a charged particle solely through electrostatic forces in three-dimensional space. This means that if a particle is placed in a position where it is balanced by these forces, it will not remain in that position without some form of external support or control. The theorem applies to systems where only static electric charges are involved. It highlights the limitations of using electrostatic forces for stable configurations, leading to the exploration of other methods, such as magnetic levitation or active control systems, to achieve stability in various applications.