The USPS spent $2.7B more than it gained in revenue from sales of stamps etc. The idea that a government agency is supposed to be profitable, and the use of the business term "lost" is appropriate, is a politicized, partisan one. (The extent to which the USA's post isn't really a government agency any more is also extremely politicized and partisan.)
One way to tell that the profitability model isn't appropriate is, what would happen if the USPS did achieve profitability? The USPS's own press release attributes $1.1B of their "loss" to a refusal by regulators to let stamp prices remain at 49 cents, requiring them to go back to 47 cents. How is a "company" that already has extremely below-market prices and can't even get regulators to permit them to keep a 2-cent increase supposed to maintain profitability, should they ever achieve it?