training bra
An undergarment worn by young, developing girls, a training bra is intended to help young girls become accustomed to wearing a bra before chest support becomes necessary. Often similar in appearance to a cropped camisole or sports bra, but provides little to no support, and so are rarely worn after breasts grow beyond a certain size.
Also known as "trainer bra" or "bralette".
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This tag implicates bra (learn more).