Dynamic Light Scattering (DLS) is a technique that uses a special instrument to measure how fast or slow particles move when exposed to light, like how a boat moves in a river. The instrument sends a light beam into a sample (a liquid, gas, or colloid) containing particles that scatter, or reflect, the light in different directions. This light reflects off the particles and then a detector measures what direction the scattered light goes in and how long it takes. The instrument can then calculate the size of the particles and the speed at which they are moving.