What is a bra size?

Answer 1

it tells you your size for a bra, just like sizes for jeans. its pretty much your boob size.

Improved answer:

Bra size consists of your band size, the band of the bra that goes around your ribcage under your breasts, and the cup size, the size of the breasts themselves. There are different ways to measure, but in general it's done by measuring just below your breasts, which gives you the band size. Then you measure around the fullest part of your breasts, and the difference between that measurement and the band size gives you your cup size. My band size is 36, and the measurement around my breasts is 14" greater, so my cup size is N. And yes, I have a very hard time finding 36N Bras.