Bite-sized means small enough to put in your mouth in one go — a piece of chicken, fruit, potato, or a sweet. Cooks cut food bite-sized so you can eat without a knife, or so a child can manage it. Writers and teachers also stretch it: a bite-sized lesson is a small piece you can take in easily, as if you were swallowing food. The home meaning is the food; the other is a picture borrowed from eating. It is ordinary, friendly English, fine at the table and in class. You will also see bite-size without the last d; it means the same.