In school notebooks wrote your grandpa and grandma, mom and dad, there are notebooks with you. But there was a time when instead of the usual us the notebooks of the students used wax tablets. Like they were on a small flat trough filled with wax. Soft wax is easily written with a sharp stick. With a sharp stick was only on the one side and on the other was dull and looked like the blade, so that it was easier to erase mistakes.
Over time, wax plates were replaced with paper notebooks, consisting of stacked four sheets and covers.
Due folded in four sheets of notebook and got its name because in Latin "tetrads" means "fourth part".