What does 'g' in switching converter input voltage \$V_g\$ stand for?
From the author (Robert W. Erickson) himself!:


  Many of the early papers in this field called it \$V_g\$, and the name stuck. I think 'g' does indeed stand for 'generator'. Certainly a more meaningful name would be preferable in an actual application.


https://www.coursera.org/learn/power-electronics/discussions/J1AxBsR2EeW_BRLjpUoXzQ

Good guess @FakeMoustache :)