1. A material used for sealing spaces between materials. 2. An elastomeric material that is used to fill and seal cracks and joints; at expansion joints, this material prevents the passage of moisture and allows horizontal and lateral movement. 3. A caulking material used to fill voids or seams for acoustical, air infiltration, or thermal purposes. 4. A mixture of polymers, fillers, and pigments used to fill and seal joints where moderate movement is expected; it cures to a resilient solid.