A word, more-so-commonly a name, used to describe people who think they are body builders that have somewhat of noticeable chest but a back that is nearly transparent; especially when viewing the person from the side.
Dude 1: Wow you see that guy with that chest?
*Guy with big chest turns to his side*
Dude 2: What guy?
Dude 1: oh shit, he disappeared!
*Guy with big chest turnsback towards them*
Dude 2: Oh, wow, he has noback.