[Trans-Am Jim]

To add to Cal's post on page one, here's my understanding of the origin of the term.

Pre WWII, the only cam grinds available were stock ones; i.e., as supplied by the manufacturer. The earliest rodders would create their own custom one-offs by welding on metal to the stock camshafts, regrinding, and then re-heat treating them, making it a "hot rod."