![1girl armpits arms_behind_head arms_up artist_request bike_shorts black_shorts blonde_hair bra chewing_gum clownpiece crotch_seam fairy_wings flat_chest full_body hat hirasaka_makoto_(style) jester_cap long_hair navel no_shirt panties_under_bike_shorts red_eyes shoes shorts solo third-party_edit touhou training_bra transparent_background underwear very_long_hair white_bra wings rating:q score:15 post #3304412](/cdn_image/preview/74/51/745140eff1f451550d99e2afc758ea8b.jpg)
A cupless bra similar to a sports bra but worn exclusively by young, developing girls. The training bra is intended to help young girls become comfortable with the idea of wearing lingerie.
Also known as "trainer bra" or "bralette".
http://en.wikipedia.org/wiki/Training_bra
This tag implicates bra (learn more).