A substance made up of tiny particles suspended in another substance, where the particles are too small to settle out like sand in water, creating a stable mixture like milk or fog.
From Greek 'kolla' (glue) + '-oid' (resembling), coined in 1860 by Scottish chemist Thomas Graham. It describes substances that appear glue-like and don't follow normal particle settlement laws.
Colloids are hiding in plain sight everywhere—your blood plasma, mayonnaise, and the clouds in the sky are all colloids. What's wild is that the same substance can be either a colloid or a solution depending on particle size, so it's all about perspective.
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