Lightning is an atmospheric discharge of electricity, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms. The Tau'ri have harnessed the power of electricity in the form of lightning on several occasions.
When faced with a broken Dial Home Device on Heliopolis in 1997, SG-1 used a metal helmet as a lightning rod to channel energy directly into the Stargate, which they then dialled manually. (SG1: "The Torment of Tantalus")
Atlantis has several lightning rods placed around the city that discharge the electrical energy of lightning strikes into four grounding stations. During a massive storm on Lantea in 2004, the Atlantis expedition disabled these grounding stations and channeled the lightning's energy through the corridors of Atlantis and into the shield generator in order to raise the shield and protect the city from destruction. (SGA: "The Storm", "The Eye")