Spackling paste

White spackle is applied to a painted surface using a small putty knife.
Spackle applied to a rough surface using a putty knife

Spackling paste or spackle is a putty used to fill holes, small cracks, and other minor surface defects in wood, drywall, and plaster. Typically, spackling is composed of gypsum plaster from hydrated calcium sulfate and glue.