You are sitting in 3rd or 4th gear. You reach a hill or want to overtake (or just feel a bit lunaticOdinEidolon wrote:errrm, what's this kickdown?

Based upon the throttle, the automatic gearbox shifts down 1 or 2 gears to give you a boost of acceleration.
A bit like a regular gearbox, dropping down a cog for these kind of things.