In a 3D game, most characters, props and scenery elements are represented as meshes, while a 2D game uses sprites for these purposes. Meshes and sprites are the ideal way to depict “solid” objects with a well-defined shape. There are other entities in games, however, that are fluid and intangible in nature and consequently difficult to portray using meshes or sprites. For effects like moving liquids, smoke, clouds, flames and magic spells, a different approach to graphics known as particle systems can be used to capture the inherent fluidity and energy. This section explains Unity’s particle systems and what they can be used for.