Specifically it is the frequency-based keyboard layout of traditional hot-metal Linotype machines. If you made a typo, the custom was to fill up the spoiled slug by running your finger down the etaoin shrdlu rows, and start fresh on the next slug. On rare occasions the layout clerk would accidentally let a shrdlu slug go to press, to the amusement of the readership.

Telegraph operators ranked the letters as etaonrish.

I always thought it was rlstne. I might be conflating English letter distribution with Wheel of Fortune letter ordering.