A base coat is a colorless substance applied to the natural nail before the application of colored polish; base coat promotes polish adhesion and reduces staining of the natural nails; in nail art, used for a background of entire nail or large areas that will be covered with another color.
(Photo courtesy of Lumos)
Required Reading
September 16, 2011
The proverbial bread in the polish sandwich, base and top coats help polish adhere to nails and prevents nails from chipping and breaking.