Lecithin is a natural emulsifier and a great stabilizer which comes from fatty substances found in plant and animal tissues. Many people unknowingly use it every day because of its presence in egg yolks.
Lecithin's emulsifying properties make egg yolks a main stay for creating emulsions, like mayonnaise and several sauces like Hollandaise. One end of the lecithin molecule binds to water and the other binds to oil, helping to strengthen and stabilize the emulsion.
To keep the strength of the lecithin at a constant, and to remove the flavor of the egg, lecithin is commonly used as a culinary powder. A common source of lecithin powder is soy lecithin, which is derived from soy beans. Lecithin powder is easily dissolved in water.
As a stabilizer in modernist cooking, Lecithin is often used in creating "airs" or other long lasting, light foams.
You can find out more about lecithin from my how to use lecithin guide or any of the lecithin articles and recipes below.