What does the bra size measurement mean?

i know the letter is for cup size, "A" being smallest cup size. by cup size, do they mean the size of the actual breast?

so what does the number mean?

i know that women have to measure twice: once for the circumference around the back and nipples, and the second time for the underboob region.

you are free to correct me, give me examples, photos, etc.
+1 y
what do you mean by back size?

also, in addition to what the measurement means, how does the number affect physical appearance. lets say you have 2 women that are a 32C and a 34C. what is the difference in physical appearance?
What does the bra size measurement mean?
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