The speed of light in a vacuum, often denoted by the constant c, is approximately 299,792,458 meters per second (or about 186,282 miles per second), and is considered to be the fastest possible speed at which matter and information can travel in the universe. It plays a fundamental role in many aspects of physics, including but not limited to the propagation of light and other forms of electromagnetic radiation, the laws of motion and electromagnetism, the properties of space and time, and our understanding of the universe at large.

The value of the speed of light has been experimentally determined and refined over the centuries, significantly influenced by scientific advancements and improvements in measurement techniques. In 1983, the speed of light was defined internationally to have an exact value of 299,792,458 meters per second based on measurements conducted using laser interference and high-precision optical setups. This definition effectively fixed the value of the meter, making the speed of light the constant standard for determining distances and lengths in the metric system.