On a small scale, all lightning is essentially the same - a channel of ionized air carrying electrical current between two differing areas of charge. The polarity of lightning discharge can affect the way it propagates and branches in space and time, but in the end, it's all an electrostatic discharge - a 'spark' in its fundamental sense. The little 'static' sparks between your finger and a doorknob are, technically speaking, the same basic process at work, just on a smaller scale. The 'types' of lightning we'll discuss here refer more to how a discharge appears to an observer, what the starting and ending terminii of the channel are, and in what direction the formation of the channel took place.