There are many definitions and uses for the term 'backless.' One
such use refers to a type of dress that doesn't have material on
the back, as in a backless evening dress.
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You should try a Backless Body Shaper or Body Briefer to be more specific, which has the benefit of being a bra and a body shaper in one, with the advantage of being backless.
This is perfect for a backless or low-cut evening outfit evening outfit or indeed a backless wedding dress.