An ideal gas is a theoretical concept in physics and chemistry that describes a gas composed of many particles that are in constant, random motion. These particles do not attract or repel each other, and they occupy no volume themselves. The behavior of an ideal gas is governed by the ideal gas law, which relates pressure, volume, temperature, and the number of particles. In reality, no gas perfectly fits the ideal gas model, but many gases behave similarly under certain conditions, such as low pressure and high temperature. The kinetic molecular theory helps explain the properties of ideal gases by focusing on the motion and energy of the gas particles.