Mayonnaise

Mayonnaise is a smooth savory sauce made from oil and the yolk of eggs. It is an emulsion in which the oil is dispersed in tiny droplets. Egg yolk contains lecithin which prevents the oil and water from separating out.

Mustard is also a good emulsifier and is frequently added. Vinegar, usually wine vinegar, or lemon juice are added for flavor and because acidity helps the emulsion to form. Garlic is a frequent addition. 

The oil used is normally a flavorless type such as sunflower oil or corn oil, but you can substitute some for a more tasty oil such as olive oil.