What is heat lightning?

Question

What is heat lightning?

Answer 1

It is lightening from a storm off in the distance.

Answer 2

Since no thunder is heard and it can often be seen even in clear sky, people often mistake 'heat lightning' as being created by the heat of the day.  But this is a common misconception.  Lightning can be seen from distant thunderstorms, sometimes from storms over 100 miles away, which is farther than the sound of thunder travels.  So simply put, heat lightning is lightning from a distant thunderstorm.