System
Also said as Game system, Interlocking mechanics, Systemic design
A set of mechanics that feed into each other, so that what one does changes what another can do. Fire burns grass, grass grows back, and wind moves fire.
Mechanics that connect produce situations nobody wrote by hand. A level has only what you built, while a system keeps surprising the people who made it.
Say it
“Do not script the burning bridge. Make wood flammable, fire spread to what it touches and rain put it out, and let the bridge burn because of those rules.”
Where you’ve seen it
The Legend of Zelda: Breath of the Wild runs fire, wind, water and electricity as rules that apply to everything: grass catches light, the heat lifts your glider, and metal draws lightning.
Not to be confused with mechanic
A mechanic does one thing. A system is what several do to each other, and the interesting part is the wiring between them.