An "expander" is a device or tool used to increase the size or volume of something. In various fields, such as dentistry, an expander can refer to a dental appliance that widens the upper jaw to create more space for teeth. This is often used in orthodontics to help correct bite issues and improve overall dental alignment. In engineering and construction, an expander can refer to a mechanism that enlarges pipes or tubes. This is important for ensuring proper fit and function in systems that require fluid or gas flow. Expanders are essential in many applications, from plumbing to manufacturing.