Caulk is a flexible material used to seal gaps and cracks in various surfaces, such as walls, windows, and doors. It helps prevent air and water leaks, improving energy efficiency and protecting against moisture damage. Caulk is commonly made from materials like silicone, latex, or polyurethane, each suited for different applications. Applying caulk is a straightforward process that involves cleaning the area, using a caulking gun to dispense the material, and smoothing it out for a neat finish. Properly applied caulk can enhance the durability of structures and contribute to a more comfortable indoor environment.