He might have been trying to express a 0 overdrive ratio. Like in some cars when the transmission ratio is 1:1. The 6 speed automatic in my cuv is direct drive in 4'th for example, An overdrive of 0.
On a bicycle we typically call it a 1:1 ratio. Which is direct drive like a penny farthing bike. A 0 overdrive might come to mind in a pinch.