The 400k is a red herring anyways. Not every engineer makes that, and not ever person who laid off was an engineer. The layoffs affected recruiters, marketing, sales, and a ton of areas that were not engineers. Lower level engineers were also targeted more than the higher level engineers, and even more importantly the hiring freezes and reductions blocked a ton of new grads from getting jobs.

There's a few definitions for it, the one I think most people default to is jobs that require physical labor.