To keep it simple, French Polishing is a finishing technique that is applied to wooden furniture and is not a polish/substance as most commonly thought.
A French Polish finish is applied with a shellac soaked cotton rubber (known as a "fad") building up layers over time using a very laborious and repetitive combination of rubbing motions. All natural materials are used throughout the polishing process to create a warmth and depth that enhances the natural grain and properties of timber.
French polishing a piece of furniture results in a superior hardwearing finish that due to the properties of the polish is also very easily repaired and maintainable.