This definition applies to both individual firms and the economy as a whole. Accounting profit is normally greater than zero from both perspectives.
Profit derives from sales to the firm's customers accommodated by credit.
Profit deriving from sales adds to net worth. Work in progress is an asset not yet sold. Profit deriving from anything other than sales is Alice in Wonderland accounting. It is accounting that counts chickens before they are hatched. Not only before they are hatched but before they are sold into final consumption.