游动 (yóu dòng) is a verb meaning 'to move or swim freely through a fluid medium—most commonly water, but sometimes air (e.g., for microorganisms or particles). The character 游 (yóu) means 'to swim' or 'to drift', evoking effortless motion; 动 (dòng) means 'to move' or 'to stir', adding the sense of active, continuous motion. Together, they emphasize smooth, unhurried, often rhythmic movement within a surrounding medium.

This word is frequently used to describe how fish, plankton, jellyfish, or microscopic organisms move in water—highlighting natural, unforced locomotion rather than purposeful travel. It can also describe floating particles in liquid or even abstract imagery (e.g., light patterns 'swimming' across a surface). Unlike the more general verb 移动 (yídòng, 'to move') or the action-oriented 游泳 (yóuyǒng, 'to swim laps'), 游动 emphasizes organic, ambient motion and is rarely used for human swimming in everyday contexts.