A bike frame is the main structure of a bicycle, providing support and shape. It is typically made from materials like aluminum, steel, or carbon fiber, which offer different balances of weight, strength, and cost. The frame connects various components, including the wheels, handlebars, and seat, allowing the bike to function properly. Frames come in various designs, such as diamond, step-through, and folding, each suited for different riding styles and purposes. The size and geometry of the frame affect the bike's handling and comfort, making it essential for riders to choose a frame that fits their body and riding preferences.