Who ever wrote that definition is not likely an engineer, and it is an engineering term. "Throttle" originated to control steam engines, a valve in the steam admission line. Close or choke down the throttle, and it reduces power output of the steam engine.
Next came gasoline engines, and the throttle controlled the flow of air/fuel mix. Similar to steam engine, valve closes down on the admission flow.
Throttle a screaming kid, slows them down too. Not considered polite nowadays!!! Again, restricting admission flow, this time it is air.
Diesels are different. No throttling going on. Lever is "speed control lever" or "governor control lever" or "power control lever" or "fuel control lever" or a bunch of others. But those are too many words, too inconvenient.
Throttle in regards to diesels is technically incorrect, but it is widely used and even accepted amongst engineers.
But engineers sitting around the table discussing a governor design, no one will say "throttle".
Kind of like the "motor" and "engine" debate!!!