What type of mixture consists of two or more liquids that don't normally mix, such as oil and water?

An emulsion is a type of mixture consisting of two or more liquids that are normally immiscible (unable to mix homogeneously). In an emulsion, one liquid is dispersed as tiny droplets throughout the other. The classic example is oil and water.

Emulsions require an emulsifying agent (emulsifier) to remain stable. The emulsifier reduces the surface tension between the two liquids, preventing the droplets from merging and separating. Common emulsifiers include lecithin (found in egg yolk, which is why egg yolk stabilizes mayonnaise), soap, and mustard. Without an emulsifier, the two liquids will eventually separate into distinct layers.

Everyday examples of emulsions include milk (fat droplets dispersed in water), mayonnaise (oil dispersed in vinegar/lemon juice, stabilized by egg yolk), and salad dressings.

A colloid is a broader category where one substance is dispersed in another, but the dispersed particles can be solid, liquid, or gas - not specifically two immiscible liquids. A suspension consists of solid particles dispersed in a liquid, and the particles are large enough to settle out over time. A solution is a homogeneous mixture where the solute fully dissolves in the solvent at the molecular level.