Built-in refrigerators are designed to be integrated into your cabinetry offering a seamless, integrated look.
Typically, these models are shallower in depth allowing them to fit flush with surrounding cabinetry and can be customized with panels that match your cabinets allowing them to virtually disappear.
Built-in refrigerators are available in a wide variety of sizes and configurations and tend to be at the top of the price range. Also, because they're meant to be integrated into existing cabinetry, most have unfinished sides.