What is a shelf bra in a swimsuit?

A shelf bra in a swimsuit is a type of built-in bra that is designed to provide support and coverage to the bust area while swimming or engaging in water-based activities. The shelf bra is essentially a band of elastic or other stretchy material that sits underneath the bust and provides lift and support without the need for straps or cups. This type of bra is common in one-piece swimsuits, tankinis, and bikinis, and is often preferred by women who want a little extra support and coverage in their swimwear. Some shelf bras may also include removable pads or cups to enhance the shape of the bust.