Chemists in the nineteenth century recognized the existence of 'misbehaving' systems: hydrated alumina, starch, dextrin and gelatin, for example. Wolfgang Ostwald grouped them into a separate category, and coined the name 'colloids' (meaning 'glue-like'). Thomas Graham showed that the constituent objects had low mobility, and became convinced that they were aggregates of smaller molecules. They could be metal particles (such as in the gold colloids made by Faraday), oxides or organic systems.

As time went on, colloids became a well-defined family of objects — more properly defined as ultradivided matter. The family has many members: soap micelles, emulsions, suspensions of solids (with sizes from micrometres to nanometres), and newborn objects such as latex particles (which can be admirably tuned in composition and calibrated in size). A common feature is that the particles are floating in a solvent; if it is not too concentrated, a colloid can flow freely, which is convenient for industry.

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