1 : an idea occurring later
2 : something (as a part or feature) not thought of originally : something secondary
Given this, what is an afterthought heel?
An afterthought heel is a technique where you first knit the "tube" of the sock, then go back afterwards to knit the heel. So simple, so easy! But wait... where do the heel stitches come from? Do you steek the heel? Get all crazy with the scissors?
This is where the magic happens.
You knit a section with some scrap yarn, then knit over it as usual. When you're ready to do the heel, you carefully pick out the scrap yarn, place the live stitches on needles, and there you are! Ready to knit the heel in the round.
But talk is cheap and not very helpful, so let's look at some pretty pictures! For now, I'm going to demonstrate this on a swatch. If I do this with a sock again, I'll post ACTUAL, REAL demo photos (OMFG!)