Caulk is a type of sealant used to fill gaps or cracks around windows, doors, and other surfaces in homes or buildings. It is made from a variety of materials, such as silicone, latex, or polyurethane, and can be applied in a bead-like shape using a caulking gun. Caulk is used to seal gaps and prevent air and moisture from entering or exiting a structure. It can also be used to fill gaps around bathtubs, sinks, and other fixtures to prevent water damage. Caulk is an important part of home maintenance, as it helps to improve energy efficiency, prevent water damage, and maintain the integrity of a building's structure.