What essential characteristic does a bi-fold door have regarding its movement?

A bi-fold door's essential characteristic is that it folds together when opened. This design allows the panels of the door to fold inwards or outwards, creating a wider opening than a traditional door. The folding mechanism facilitates smooth movement and maximizes space, making it a popular choice in areas where maximizing light and openness is desired, such as in living rooms or between indoor and outdoor spaces.

The folding action distinguishes bi-fold doors from other door types that operate through sliding along a track or swinging on hinges, which limits their ability to create a large passageway. The effective use of hinges and panels in a bi-fold design enables versatility in configuration and aesthetics, contributing to its appeal for architectural applications.