What is arson?

Arson happens when someone purposefully burns someone's house. Note that the defendant doesn't need to burn down the house. Any amount of burning beyond basic scorching is sufficient to be arson. It's sort of like when you're trying to light a campfire and you hold the flame on the log, which scorches the log, but doesn't quite cause the log to catch fire... that isn't enough to be arson. But the second the log catches fire and burns by itself, arson has been achieved.