What is "Confidence" even supposed to mean?

Too many "artists" crow on about "confidence", the apparent state of being "confident" as well as the supposed struggle of avoiding it's opposite. Terms such as "Confident Lines", "Confident Shapes", "Confident Anatomy", "Confident Values", "Confident Composition", "Confident Colours", et cetera are bandied about often. Curiously enough, not one is able to give a concise and coherent definition and/or a rational explanation of this "confidence" spectre, never mind why anyone should bother with chasing it.