gate-to-gate? help to understand

hello All!
I design the matching network for push-pull amplifier and can't understand what is gate-to-gate connection.
Could anybody explain me with it?

ZSOURCE = Impedance of the external input matching circuit as seen
from gate to gate.
I can"t understand 'gate-to-gate' . Each of two gates see impedandce of the external input matching circuit ZSourse. Am i wrong?