Self-focusing is a phenomenon where a beam of light or other waves, such as sound or electromagnetic waves, can concentrate itself into a smaller area as it travels. This occurs due to the nonlinear interaction between the wave and the medium it passes through, which can cause the wave to change its speed and direction. In optics, self-focusing can lead to the formation of light filaments, where intense light beams maintain their shape over long distances. This effect is important in various applications, including laser technology and fiber optics, as it can enhance signal quality and efficiency.