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The speed of light in a vacuum, denoted by the symbol 'c', is a fundamental physical constant. It represents the maximum speed at which all forms of electromagnetic radiation, including light, can travel. This constant plays a crucial role in many areas of physics, including special relativity, where it links space and time, and in the famous mass-energy equivalence equation, E=mc². Its value is precisely defined and universally accepted.

Historically, scientists like Ole Rømer, Hippolyte Fizeau, and Albert A. Michelson conducted experiments to measure the speed of light. However, it was eventually defined as an exact value to standardize the definition of the meter. The current definition of the meter is based on the speed of light, stating that a meter is the distance light travels in a vacuum in 1/299,792,458 of a second. This makes the speed of light in a vacuum exactly 299,792,458 meters per second.

For most practical purposes and calculations, this value is often approximated as 3 × 10^8 meters per second. This approximation is widely used in physics and engineering problems because it is very close to the exact value and simplifies calculations significantly without introducing substantial error for many applications.