Definition

Scissor:

A movement, usually danced by the man, in which an extended leg is withdrawn and crossed in front of the supporting leg without weight so that it remains free for the next step or movement. May also refer to a figure in which the man steps forward in outside position (left or right) caressing the outside of the lady’s leg with his leg (as in 3 of basico), then crosses behind himself which pushes the lady’s leg to cross in front. May also refer to a jumping step from stage tango where the lady swings her legs up and over with the second leg going up as the first leg is coming down (frequently seen as an aerial entry to sentadas).

(from tangoafficionado.com (http://www.tangoafficionado.com/tango_terminology.htm))