A style of tango where the woman has her back against the front of the man, and so both their fronts face the same direction.
A reference is Antonio Todaro. He had a special fondness for dancing as follower and as an innovator, he had fun expanding the follower's part. He is also famous for his skilled Tango Doble Frente / double front (tango al reves - inversed/reversed) in which the woman has her back to the man and the man embraces her around the waist, so both dancers face the front/public, it is a very historical style of tango invented by the popular milongueros of the 1940s. All steps that one dances in the regular, or derecho position, can be danced al reves.
from Tango-E-Vita (http://users.pandora.be/Tango-E-Vita/go2_bestanden/Tango-E-Vita.htm)