A simulation is the representation of the operation of a real-world process or system over time. Simulations require the use of models; the model represents the key characteristics or behaviors of the selected system or process. This definition of simulation is slightly wider than the usual definition; it doesn't necessarily involve a step-by-step simulation. It is sufficient that characteristics of the evolution of the "simulated" process are captured sufficiently to make predictions about outcomes of the simulation. This matches the colloquial use when talking about intelligent systems "simulating" external processes or other agents.

This tag is about concrete simulations and differs from the following more specific tags as follow:

Simulation Hypothesis concerns whole-universe simulations and anthropic and philosophic arguments.
Whole Brain Emulation is about the simulation of a whole human brain, potentially at higher speeds.
AI Boxing is the simulation of the world for an AI such as to learn about its actions and capabilities without risk to the real world.
Simulator Theory is a way to interpret the operation of large language models.
Agent Simulates Predictor is a problem for capable agents proposed by Gary Drescher.