A sexual position, where 2 girls do the postion 69, and two guys are penetrating on either side (1 - 69 - 1)

Everyone knows what a 69 is... if you don't.

Your on 'urban dictionary'- you know what to do =F

Anyways, a 1691 is your traditional 69 with two people watching, normally lying/standing lifelesss... just taking it all in.