The acronym GTN stands for Gross To Net. It is a process that calculates and determines an individual's net pay. It is done by subtracting all expenses, such as deductions, taxes, etc., from an individual's gross income.
Gross pay or Gross Income is an individual's monthly income before factoring in things such as taxes, deductions, benefits, etc.
Net pay or Net Income is whatever money an individual has left after excluding all sorts of deductions from it and factoring in all sorts of benefits.