OP-AMP with varying Vee
The label in the diagram refers to the wiper of the potentiometer, which is connected to Vee. The two outer terminals are connected to the offset-null of the Op Amp. The offset null terminals allow you to calibrate an op-amp to ensure the output is exactly zero at exactly equal inputs, despite manufacturing tolerances, by altering the position of the potentiometer. This arrangement where the wiper is connected to Vee and the other two terminals to the offset-null terminals is the most common arrangement of this facility.