"rendering" the music and some of the graphics.
I think that's what's called procedural audio/graphics. For audio, it's like building synthesizers into the game, to then be able to play the music/fx as a program (sort of like sheet music) instead of an audio file.
And even in some prototype bus, the Gyrobus, in the 50's that used an electrically charged flywheel that was also (to some degree) regeneratively recharged when breaking:
Source: Wikipedia: Gyrobus