Refer to figure.
LIGHTNING
As a towering cumulus develops, a large electrical charge separation builds up within the cloud. Lighting results when this electrical charge becomes strong enough to jump from the cloud to the ground, to another cloud, or to an opposite electrical charge within the same cloud.

In the early stages of development, air acts as an insulator between the positive and negative charges in the cloud and between the cloud and the ground. When the opposite charges build up enough, this insulating capacity of the air breaks down and there is a rapid discharge of electricity that we know as lightning.

• Intra-Cloud lightning: The most common type of lightning. It happens inside the cloud, jumping between different charge regions in the cloud. It lights up the cloud to look like the picture above.
• Cloud-to-air lightning: Referring to a discharge (or a portion of a discharge) jumping from a cloud into clear air. This happens when negative charged air particles become attracted to positive charges within a cloud.
• Cloud-to-cloud lightning: Happens when a negatively charged cloud finds a positively charged cloud and opposites attract. The discharge travels from cloud to cloud.
• Cloud-to-ground lightning: Occurs between the cloud and the ground.