Where the words come from
Explicit and implicit costs, accounting and economic profit, and how entry and exit push a competitive market to zero economic profit in the long run — Principles of Economics 2e, OpenStax, licensed CC BY 4.0. https://openstax.org/books/principles-economics-2e/pages/7-1-explicit-and-implicit-costs-and-accounting-and-economic-profit and https://openstax.org/books/principles-economics-2e/pages/8-3-entry-and-exit-decisions-in-the-long-run. Changes: "zero economic profit" and "economic profit" relabelled normal and supernormal profit; "retail store" to "shop"; the Fred law-practice example and its dollar figures replaced with an invented café; the entry passage condensed and its red-cape image dropped; the four card definitions lifted from 7.1, "only" added to accounting profit; the café card examples, the mistake note, exam tip and checks are ours; British spelling.
The normal rate of profit a firm should expect to earn, and a normal level of profit in the long run — Principles of Economics 2e, OpenStax, licensed CC BY 4.0. https://openstax.org/books/principles-economics-2e/pages/11-3-regulating-natural-monopolies and https://openstax.org/books/principles-economics-2e/pages/9-1-how-monopolies-form-barriers-to-entry. Changes: The phrases recast into the definition of normal profit; the rest of both sections not used.
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