Casing refers to the protective structure installed in a wellbore during drilling operations. It is typically made of steel or other durable materials and serves to stabilize the well, prevent contamination of groundwater, and isolate different geological layers. Casing is essential for maintaining the integrity of the well and ensuring safe extraction of resources like oil and gas. Once the drilling is complete, the casing is cemented in place to provide additional support and seal off any potential leaks. This process is crucial for the safety and efficiency of operations in the oil and gas industry, as it helps manage pressure and prevents environmental hazards.