1) A door is a panel that covers an opening and provides warmth, security, privacy, elegance, and protection from weather for a building. 2) When choosing doors, home owners should consider the room, material strength for security, style, functionality, sound insulation, and durability. 3) Common door types include wooden, glass, steel, PVC, fiberglass, and aluminum doors, categorized based on material, door component construction, and working function like swinging, sliding, or revolving doors.