Why is it called QPTL?

The name QPTL is an acronym for Québec Payroll Tax Library.  According to Wikipedia, "In computer science, a library is a collection of implementations of behavior, written in terms of a language, that has a well-defined interface by which the behavior is invoked. This means that as long as a higher level program uses a library to make system calls, it does not need to be re-written to implement those system calls over and over again."  In simpler terms, QPTL is a library of computer programs that can be used by another computer program to calculate payroll withholding deductions for Québec employees and employers.