Variety is a single card bingo  - the first with moving numbers!  In this case, Magic Lines.  Magic Lines allow you to move the first three columns of numbers (on this game) up or down one position.
This increased the winning potential for players, and really opened up Bally to experiment with different designs and player-friendly features.  The fixed numbers on earlier games of course allowed for complex gameplay, but this innovation really took things to another level.
Backglass:

Cabinet:

Playfield:

Flyer describing Magic Lines:
http://bingo.cdyn.com/machines/bally/variety/resources/fly-variety-2.jpg