Virtual thing to “run,” for short

SIM

Think of a three-letter prefix used in games or training to mimic real-world scenarios, like flying or driving.

The clue plays on the idea of "running" something in a virtual sense, like a simulation. "For short" hints that the answer is an abbreviation, and "SIM" is short for "simulation," which fits perfectly. It’s a straightforward tech reference—no hidden wordplay, just a concise nod to digital environments.