speed of light
- (physics) The speed of electromagnetic radiation in a perfect vacuum: exactly 299,792,458 metres per second by definition.
2011 September 22, Nick Collins, “Speed of light 'broken' by scientists”, in Daily Telegraph:
- The science world was left in shock when workers at the world's largest physics lab announced they had recorded subatomic particles travelling faster than the speed of light – a feat that Einstein said was impossible.
- (colloquial, figuratively) A very rapid speed.
the speed of electromagnetic radiation in a perfect vacuum