Infinite Sets. If you continue to study this subject you will find discussions about infinite sets, and the idea of different sizes of infinity. That subject has special names like Aleph-null (how many Natural Numbers), Aleph-one and so on, which are used to measure the sizes of sets.
For decades, glossy paper, the type used in magazines, was made using a white clay called kaolin (named after the Chinese region Kao-Ling where it was mined to produce porcelain).
Freesheet paper is free of groundwood pulp and has a bit higher brightness (whiter) than groundwood paper. Freesheet starts at a number 3 grade. Magazines commonly use 50#, 60#, 70# text weight freesheet options on the interior and 80#, 100# text weight or 66# cover weight freesheet stock on cover options.