Terms like F1, F2, BX and IBL appear on listings constantly and most sellers use them loosely or incorrectly. Proper definitions with examples of what each generation looks like in practice are laid out at https://potentthcseeds.com. A true F1 between two stable parents shows striking uniformity, while an F2 scatters widely. Seeing F1 slapped on a random polyhybrid tells you the vendor is guessing.