What is the speed of light in vaccum?

CONCEPT:

• Light is a form of energy that produces the sensation of vision.
• By the term light, we usually mean Visible Light i.e. 

"VIBGYOR" it stands for Violet, Indigo, Blue, Green, Yellow, Orange, Red.

• Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be perceived by the human eye.
• Visible light is usually defined as having wavelengths in the range of (400-700) nm.
• This wavelength means a frequency range of roughly 430-750 terahertz.

EXPLANATION:

• Speed of light: The speed of light in a vacuum commonly denoted c, is a universal physical constant important in many areas of physics. Its exact value is defined as 299792458 meters per second (approximately 300000km, or 186000 mi/second or 3 × 10⁸ m/s).
• It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time interval of 1/299792458 second.

​Additional Information

• speed of light is different in a different medium