Caulk/kɔːk/ Definition 1 of 2Pro Tip 1/3Home Repairs Caulk is often used in contexts related to fixing things around the house. I need to caulk the bathtub to stop water leaking. Pro Tip 2/3Preventative Measure Caulking is a proactive step to avoid damage, like preventing wood rot. They caulked the wooden deck to protect it from rain. Pro Tip 3/3Weatherproofing Caulk is used to seal buildings against weather, especially in windows and doors. You should caulk the doorframe before winter arrives.