Lightning is amazing stuff. It is actually made of electricity, that builds up in clouds because all the bits of clouds are bumping into each other during a storm. When the build up of electricity becomes too big, it has to go somewhere: so that’s why you see bolts of lightning coming down from clouds to the ground. A lightning bolt is incredibly hot: about 30,000 degrees, which is hotter than the surface of the sun!
Thunder is the name given to the sound of lightning. When lightning hits the ground, it is so hot and fast that it makes a little hole in the air. The sound of thunder is the air rushing back into the hole and banging together.