Tack-free is a commonly used term for nail products (specifically top coats) that describes a product that does not have the sticky, inhibition layer. This layer is uncured monomers where curing is inhibited by the presence of oxygen. Tack-free describes a product that has a higher percentage of photoinitiators so most of the monomers are cured. However, there will always be some degrss of uncured material on the surface which should be carefully removed by a cleanser