An annular preventer is a crucial safety device used in drilling operations to control well pressure. It is designed to seal around the drill pipe or casing, preventing the escape of fluids and gases from the well. This helps to avoid blowouts, which can be dangerous and costly. The annular preventer operates by using a rubber sealing element that can expand and contract. When activated, it creates a tight seal, allowing for safe drilling and maintenance. These devices are part of the larger category of blowout preventers (BOPs), which are essential for managing well control during drilling activities.