one size smaller than your actual size.
used to inform friends who want to give you clothes what size you want, but they'll get you a size larger, so it fits.
Eric: Hey Dave, I'm going to Abercrombie and Fitch. Lemme get you something. what's you size?
Dave: Uhhhh.... XL.
Eric: Brand Name XL?
Dave: ....Yes.
Eric: I'll get you a XXL.
Brand Name Size should not actually include saying 'size'.