underbust
Underbust is a term used for garments of clothing that go around and under the bust, accentuating the breasts and revealing whatever might be worn underneath. The edge of the outer garment should ideally rest just underneath the bust.
Some clothing styles that incorporate this feature are maid uniforms (particularly from the Anna Miller and Koubeya restaurant chains), the dirndl, most corsets, and the virgin killer outfit.
For clothing that encloses all sides of the bust, use framed_breasts.