It stands for "pokertracker". In limit poker win rates are typically measured in big bets (bb)/100 where a big bet is 2x the big blind. But since there's no such thing as a fixed bet in NL pt uses big blind as the measure. So to distinguish between LHE "bb" (big bet) and NL "bb" (big blind) he added "pt" to the NL one. In later versions of pt he's added an option on prefs tab since some ppl don't like "ptbb".
