When the C/SCSC came out in the United States in the late 1960s to early 1970s, the Department of Defense insisted that organizations with whom they did business had a fairly advanced project management information capability. Because this insistence was attached to large amounts of business, companies took notice and quickly put into place the codified project management practices called for in C-Spec.
Coming as it was from the United States Department of Defense, you just knew there would be plenty of acronyms.
The time-phased budgets were known as the budgeted cost of work scheduled, which quickly became BCWS and shortened again to just "S."
Similarly, earned value was the budgeted cost of work performed, abbreviated to BCWP and then "P."
Actual costs, being the actual cost of work performed, then ACWP, had the same last initial as earned value, so it became just "A."
Three of the most important concepts in project management information theory had been reduced to single letters. It could even be argued that this entered the realm of code: a code that only the true believers of project management knew by heart.
But there was no earthly reason to know what the project managers were talking about if you were a newly minted MBA or an accountant.
Their faces would likely assume aspects not unlike those of archeologists trying to understand hieroglyphics pre-Rosetta Stone.
Project managers could discuss their cost and schedule performance openly, even the ugly parts, without fear that the non-believers of project management had a clue what was being asserted.
Indeed, the folks in accounting took the opposite tack. Their communications lost their original precise definitions and are now mainstream. The "bottom line," originally the last line of information on a profit and loss statement, entered the business lexicon and eventually became synonymous with the final outcome of a process or event.
But you know you're in the company of project managers if you overhear a discussion on the merits of the CPI and SPI at the cume level (the reporting of the schedule performance index and the cost performance index at the cumulative, or life-cycle-to-date, level). The Defense Acquisition University actually publishes a "Gold Card," which is, in essence, our secret decoder ring, defining most of the commonly used project management acronyms and formulae.
At least we have the "Gold Card." What do y'all think?