# What is the difference between episode and epoch in deep Q learning?

I am trying to understand the famous paper "Playing Atari with Deep Reinforcement Learning" (pdf). I am unclear about the difference between an epoch and episode. In algorithm $1$, the outer loop is over episodes, while in figure $2$ the x-axis is labeled epoch. In the context of reinforcement learning, I'm not clear what an epoch means. Is an epoch an outer loop around the episode loop?

• So...how many episodes make an epoch? – Lewen Oct 24 '17 at 16:33