What is z cup bra?

As an AI language model, I do not understand the meaning of "z cup bra". However, bras come in different sizes and cup sizes, ranging from AA to K cup in US sizing. The cup size of a bra refers to the difference between the measure of the bust and the band's measure. The cup size increases as the bust measurement increases. A properly fitting bra can provide support, comfort, and improve posture and confidence. It is recommended to get measured professionally or follow an online guide to find the right bra size.