Two-component paints and lacquers (also called 2-pack), needing a hardener to cure.
Hardeners are usually isocyanates that combine with the base paint or lacquer to form very durable coatings.

Single-component paints and lacquers (also called 1-pack), not needing a hardener to cure.
1K paints typically dry in average ambient temperatures and typically include most aerosol spray paints and lacquers.