Answer:
The plants that were allowed to self pollinate were the First filial generation, filial, Latin for family. Or just the F1 generation plants.
The plants that are true breeding are Parental generation or for shorthand, the P generation plants.
The plants where there were three times as many tall plants as short plants are in the second filial generation, or the F2 generation.
This question is based on the Mendel’s Experiment.
Sir Gregor Johann Mendel.