ZP is referring to Zing Points and we have introduced this into our Junior and Teen program to make them more engaging. You acquire your ZP every time you complete a set of exercises. The points you are awarded are not based on how the exercise is rated but by completing them.
You can earn more points depending on your Zing streak, so if you are doing both sets of exercises everyday you will start to see an increase in the amount of Zing Points you are awarded.