Similar to the word previously defined by me (and was stolen by this other guy, how original of you), BNWT, this means Brand New Without Tags. It indicates that the particular item for sale is brand new (supposedly never worn, although there are liars out there...), however the tags have been removed.

the thing that you don’t have when you’re phones percentage is over 20

Acronym for "Brand New Without Tags". Seen primarily on auction sites such as eBay.

Similar to BNWT