Explain SMBC — the wiki for Saturday Morning Breakfast Cereal

This comic features a child asking their mother "Mommy, what's a 'size zero'?" The mother explains that size zero is a term for women's clothing sizes, which have to do with the circumference of the wearer. She then takes the concept to its logical mathematical extreme: in cylindrical coordinates, a size zero would mean zero radius, which would collapse all angles to the same value, meaning size zero women would "exist in one dimension of space given by her height." The child responds "Huh. I see." and the mother offers the alternative: "Either that or women's sizing metrics are absurd."

The joke plays on the absurdity of women's clothing sizes, particularly the concept of "size zero," by applying rigorous mathematical reasoning to the naming convention. If you model a human body as a cylinder (which is roughly what clothing sizes do by measuring circumference), then a circumference of zero implies a radius of zero, which means the person would be a one-dimensional line -- just a height with no width. The comic uses this mathematical reductio ad absurdum to highlight how nonsensical women's clothing size numbering is, since "size zero" obviously doesn't literally mean zero circumference. The mother's dry delivery and the final aside about women's sizing being absurd serve as a commentary on the fashion industry's arbitrary and often criticized sizing system.