The speed of light in a vacuum is approximately 299,792 kilometers per second (or about 186,282 miles per second). This constant is denoted by the symbol "c" in physics and plays a crucial role in various theoretical frameworks, including Einstein's theory of relativity. The speed of light determines the limits of how fast information and matter can travel in the universe, influencing concepts of space, time, and causality. It is instrumental in understanding electromagnetic radiation, gravity, and the behavior of particles at high velocities, making it a fundamental aspect of modern physics and cosmology.