A device dubbed a "drone" can actually be classified into two broad categories. The first is a fully autonomous vehicle that can fly without human intervention. The essential parts of a drone are,
Gyroscope: A small sensor that detects which way your device is facing. Ensures that your drone moves precisely how much you want it to.
GPS: Your drone would have no idea where or where it is going if not for all of those satellites.
Processor: Every year, the computer that powers everything gets faster and more energy-efficient, and the same companies that make them also make drone-specific ones.
Camera: Every advancement in resolution and computation makes your drone smarter, safer, and more self-sufficient.