In KiCad (Pcbnew), and perhaps other PCB layout programs, there is an Eco1.User layer and also an Eco2.User layer.
What does the "Eco" stand for? And what are these drawing layers typically used for, in particular, do they have an "official" purpose?
Google doesn't turn up much on the topic, although I found alternate spellings ECO1 and E.C.O. 1.