Answer:
If you hear thunder and then see lightning at almost the same time, this means that the lightning was likely close by. Thunder is the sound created by lightning, which is the discharge of energy between two clouds or between a cloud and the ground. Because sound travels much slower than light, it takes longer for the thunder to be heard, which is why we usually hear thunder after seeing a flash of lightning. This indicates that the lightning was very close in proximity and that you should be aware of the potential danger of an impending thunderstorm.