The movement of liquid or gas particles from a high to low concentration is called diffusion.

Here's a breakdown:

* Diffusion is the spontaneous movement of particles from an area of high concentration to an area of low concentration. This happens because particles are constantly in motion and tend to spread out to occupy all available space.

* Concentration refers to the amount of a substance in a given volume.

* High concentration means there are many particles packed closely together.

* Low concentration means there are fewer particles spread out over a larger area.

Think of a drop of food coloring in a glass of water. The food coloring particles are highly concentrated in the drop. Over time, these particles will diffuse throughout the water, spreading out to reach a more even concentration. This is diffusion in action.