A bi-fold door is a type of door that consists of two or more panels that fold in on themselves when opened. This design allows for a wide opening, making it ideal for connecting indoor and outdoor spaces, such as patios or balconies. Bi-fold doors are often made of materials like wood, aluminum, or vinyl, and can be customized in various styles and finishes. These doors operate on a track system, which enables smooth movement and easy access. They are popular in modern architecture for their aesthetic appeal and functionality, providing natural light and enhancing the flow of space in homes and commercial buildings.