Sorry - should have defined the terms a little better
PR is usually the number that one sees when they look at the Google toolbar or one of its clones - which Google has made pretty much useless in an attempt to thwart link buyers wheras Page Rank is the actual part of the Google algorithm (actually the main basis of their voting system) used to rank pages against each other.
These are the "standard" definitions however you are correct in that a lot of people use them interchangeably - hope that helps