Burnout is this weird concept that developers have invented to describe "I can't be bothered to keep going"

You are not serious, or you haven't been through a burnout. A burnout is probably not due to a lot of work, but to bad conditions/results/consequences. You can get burnt out without working (or working too little), and burn out is more than "I can't keep going". It's a mind disturbing thing and can be quite serious and lead to a depression.