What is nenosecond?

Answer 1

I assume you mean nanosecond. The prefix nano- means "one billionth of" or "multiplied by 10-9". So a nanosecond is 10-9 seconds or one billionth of a second.

As the speed of light is 299 792 458 m/s, a nanosecond is the time a beam of light would take to travel 0.299 m or (essentially) 30 cm or 1 foot