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).
What you will be looking for when you identify it is a super flat, ultra smooth and very glossy paper. Generally you will find the flip side to be plain white or white matte. You can find Cast Coated two side glossy papers but they are not as common as the one sided.