General Atomics MQ-9 Reaper in the context of "UCAV"

An unmanned aerial vehicle (UAV) or unmanned aircraft system (UAS), commonly known as a drone, is an aircraft with no human pilot, crew, or passengers on board, but rather is controlled remotely or is autonomous. UAVs were originally developed through the twentieth century for military missions too "dull, dirty or dangerous" for humans, and by the twenty-first, they had become essential assets to most militaries. As control technologies improved and costs fell, their use expanded to many non-military applications. These include aerial photography, area coverage, precision agriculture, forest fire monitoring, river monitoring, environmental monitoring, weather observation, policing and surveillance, infrastructure inspections, smuggling, product deliveries, entertainment and drone racing.

An unmanned combat aerial vehicle (UCAV), also known as a combat drone, fighter drone or battlefield UAV, is an unmanned aerial vehicle (UAV) that carries aircraft ordnance such as air-to-surface missiles, anti-tank guided missiles (ATGMs), and/or aerial bombs on hardpoints or within weapons bay, allowing it to perform tactical attacks known as drone strikes. UCAVs are used for intelligence, surveillance, target acquisition and reconnaissance, attacking high-value targets and prolonged loitering before needing to return to base, unlike kamikaze drones, which are single-use drones made for physically ramming into a target and exploding on impact; or surveillance drones, which are unarmed drones used only for aerial reconnaissance and gathering intelligence.

Aircraft of this type have no onboard human pilot, but are usually under real-time remote control by human operators, with varying levels of automation. As the operator runs the vehicle from a remote terminal via radio control, equipment necessary to support an on-board human pilot is not needed, resulting in a lower weight and a smaller size than a manned aircraft for the same payload. Many countries have operational domestic UCAVs, and many more have imported fighter drones or are in the process of developing them.

Targeted killing is a form of assassination carried out by governments outside a judicial procedure or a battlefield.

Since the late 20th century, the legal status of targeted killing has become a subject of contention within and between various nations. Historically, at least since the mid-eighteenth century, Western thinking has generally considered the use of assassination as a tool of statecraft to be illegal. Some academics, military personnel and officials describe targeted killing as legitimate within the context of self-defense, when employed against terrorists or combatants engaged in asymmetrical warfare. They argue that unmanned combat aerial vehicles (drones) are more humane and more accurate than manned vehicles.