Board Thread:Consensus track/@comment-6608101-20130412202347/@comment-4057437-20130621080920

Btp, PTP and FTP are online MMO terms: Buy To Play (you only pay once), Pay To Play you pay to play by subscription, often by the month, Free To Play are games that cost nothing to play (they usually get their income by selling special ingame items that sometimes can be earned by dilligent, skilled play).

As for NPC, this Wiki states in the style guidelines that the term 'player' is to be avoided, so Non Player Character is already a no-no.

However, you got our point, not all players know these terms, especially non native English speakers.