What is "millions of frames" in the plots in the paper?

[p3achyjr]

Hello, thank you again for the paper and the associated code :)

I noticed that in the paper, most plots use "millions of frames" on the x-axis:

What does this metric mean? Is it number of NN queries, number of games, training examples, or something else entirely?

[fidlej]

Thanks for asking. It is the number of frames generated by the environment. For example, on Atari, we count also the skipped frames.