In a 3D game, most characters, props and scenery elements are represented as meshes, while a 2D game uses spritesA 2D graphic objects. If you are used to working in 3D, Sprites are essentially just standard textures but there are special techniques for combining and managing sprite textures for efficiency and convenience during development. More info
See in Glossary 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 systemsA component that simulates fluid entities such as liquids, clouds and flames by generating and animating large numbers of small 2D images in the scene. More info
See in Glossary can be used to capture the inherent fluidity and energy. This section explains Unity’s particle systems and what they can be used for.