An Unmanned Aerial Vehicle (UAV) is an aircraft that has the capability of autonomous flight, without a pilot in control. Amateur UAVs are non-military and non-commercial. They typically fly under “recreational” exceptions to FAA regulations on UAVs, so long as the pilots/programmers keep them within tight limits on altitude and distance. Usually the UAV is controlled manually by Radio Control (RC) at take-off and landing, and switched into GPS-guided autonomous mode only at a safe altitude. (Confused by all the acronyms and unfamiliar terms in UAVs? A glossary is here.)
---1) An RC plane, muticopter (quadcopter/hexacopter/tricopter, etc) or helicopter (see good starter plane options here). You can buy them ready to fly, including autopilot, here.
---2) An autopilot, such as APM 2.6 (see below)
---3) Optional: a useful “payload”, such as a digital camera or video transmission equipment
The DIY Drones community has created the world's first "universal autopilot", ArduPilot Mega (APM). It combines sophisticated IMU-based autopilot electronics with free Arduino-based autopilot software that can turn any RC vehicle into a fully-autonomous UAV.
A full setup consists of:
You can buy Ready-to-Fly UAVs (both planes and multicopters) from 3D Robotics: