An emulsifier is a substance that helps stabilize and mix two immiscible liquids, such as oil and water, by reducing surface tension at their interface. It contains both hydrophilic (water-attracting) and hydrophobic (water-repelling) properties, allowing it to interact with both types of liquids. Common examples of emulsifiers include lecithin, found in egg yolks, and various food additives like mono- and diglycerides. Emulsifiers are widely used in food products, cosmetics, and pharmaceuticals to create stable emulsions.