A "bandeau" top is a short tube top usually paired up with a bottom piece to make a bikini. Called a "bandeau bikini", it offers all the support of a Republican at a drag queen convention, and has all the aesthetic appeal of a conversion van.
It squeezes girly bits (meaning boobs...) into unnatural positions, and overall is not a good choice to wear to the beach, to class, or to anywhere in general. It reduces the amount of tan lines one gets, but it's not worth the risk of unintentionally ending up "roaming free". At least this noder doesn't think so.