This this this, so much this. The economic definition is for a “perfectly competitive market,” one with extremely low barriers to entry. And one of the argumen

This this this, so much this. The economic definition is for a “perfectly competitive market,” one with extremely low barriers to entry. And one of the arguments about these markets is that they are the least profitable markets because firms in a less-profitable market will want to jump the extremely low barriers to switch into that market; this dilutes per-firm profits in the competitive market and concentrates them in the less-competitive market. Economists consider those least-profits an “opportunity cost” of spending your time in the first place, and if you include that as an explicit cost then the “profit” is indeed zero.