There are three types of garage doors: One-piece, roll-up, and sectional. The focus of this introduction is on the most common type, sectional garage doors.

Sectional doors are so designated because they are made of sections. Residential doors normally have four or five sections, but the newer coach house doors often have only three. Commercial and industrial doors normally need 14 feet of door height to accommodate tractor-trailer rigs. Hence doors comprised of seven 24" high sections are probably the most common, though higher doors are often needed.

Garage door sections are stacked vertically. They are held together with hinges along the length of the sections. The hinges at each end not only hold the sections together, but they serve an additional purpose of holding the rollers in place. Rollers are needed to allow the door to be opened and closed in tracks. These tracks are attached with track brackets to the sides of the opening called the jamb. These brackets are also called jamb brackets.

The end hinges also serve a third purpose - to allow the door to close into a wedge. The end hinges follow a progression - 1,2,3,4,5,6, etc., with each higher number spacing the roller further away from the hinge. The vertical track assists in this wedge action by using graduated track brackets, with lower-numbered jamb brackets holding the bottom of the track closer to the jamb while the higher-numbered brackets keep the top of the vertical track further away from the jamb. The net result is a garage door that seals tightly against the opening. This hardware was originally patented by Overhead Door Corporation, and for several decades a lot of ingenuity went into getting garage doors to seal against the openings.

Hinges allow the sections to pivot as the garage door opens, but no hinges are needed at the bottom of the bottom section or at the top of the top section. Hence other hardware is used. At each end of the top section is a top fixture or top bracket that holds the roller in position in the track. At each end of the bottom section is a similar bracket that holds the bottom rollers in place. This bottom bracket, or bottom fixture, also holds the cable used in counterbalancing the door.

Garage doors are designated by many names. In residential applications the almost universal designation is garage doors. In commercial and industrial applications the designations vary widely. The term, "overhead door," generic for Overhead Door Corp., is probably the most common. It designates the big overhead-type doors that travel back in tracks over the dock area where over the road trucks unload. Building maintenance engineers and purchasing agents often use the term "sectional doors" to contrast them with roll-up type steel rolling doors or one piece pedestrian doors. Similarly, the "big outside door" stands in contrast to the smaller doors - both inside and outside. "Dock doors" designates the doors on the loading dock, which may be sectional or rolling; these stand in contrast to the "big outside doors." Apartment and condominium owners refert to the parking garage door. One manufacturer referred to their doors as "overdoors."