In statistical physics, the microcanonical ensemble is a theoretical tool used to analyze an isolated thermodynamic system. In such a system, the macrostate of the system has a fixed given energy and there is one and the same probability for every accessible microstate. The microcanonical ensemble is also called the NVE ensemble because it describes a system with a fixed number of particles, a fixed volume, and a fixed energy .
Read more about Microcanonical Ensemble: Terminology, The Microcanonical Ensemble, Entropy, Classical Mechanical Systems, Connection With Liouville's Theorem, Ergodic Hypothesis