Preferment = a pre dough ferment; perhaps better hyphenated pre-ferment!
Pre = Before Main Dough; Ferment = Fermentation
In other words a pre-ferment is a ferment before the main one. Be it starter, levain, poolish or biga but not an autolyse as that should have no starter or levain and even if it does its the beginning of the final dough.
“Things” done before the main fermentation could mean anything and might make one think an autolyse is included.
I normally autolyse without starter or yeast. The Tartine book 3 also references that autolyse is just water and flour. As well, I found this method with many references.
Having said that, I read that yeast is included in the autolyse process in a few recipes, I wonder why. This would be overproof or over ferment, right?
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Could be any number of reasons and I couldn’t venture a guess until i saw the recipe.
For instance, one reason might be is ease of mixing. Another might be for timing.
Over proof or over ferment would apply to the final dough if left too long and the final shaped loaf rises too much or the yeast runs out of food, respectively.
Important to note that once the yeast goes in effectively the bulk ferment starts and the clock is ticking.