a robe: the long outer garment pulled on over other clothing as a mark of rank or dignity
A robe of this kind is the outer layer, the long garment worn over the tunic. It is not everyday work clothing but a sign of standing, worn by prophets, princes, priests, and kings. Because it sat on top and hung loose, it is the garment people reach for in the Bible's most charged moments: Jonathan strips off his own robe and gives it to David, David quietly cuts a corner from Saul's, and grieving men tear theirs.
The same garment, made in blue and hemmed with golden bells and pomegranates, becomes the high priest's official robe worn with the ephod. It is still simply the outer robe, but set apart for service at the altar, which is why the instructions in Exodus describe it in such careful detail.
Because the robe was the visible layer that announced who a person was, the prophets and poets turn it into a picture: a person can be wrapped in righteousness, in zeal, or in shame the way a body is wrapped in a robe. The image works precisely because everyone knew the robe as the garment you put on to be seen.