Loitering munition
The following table compares similar size-class cruise missiles, loitering munitions, and UCAVS:

Whereas some cruise missiles, such as the Block IV Tomahawk, have the ability to loiter and have some sensory and remote control features, their primary mission is typically strike and not target acquisition. Cruise missiles, as their name implies, are optimized for long-range flight at constant speed both in terms of propulsion systems and wings or lifting body design. They are often unable to loiter at slow fuel-efficient speeds which significantly reduces potential loiter time even when the missile has some loiter capabilities.
Conversely almost any UAV could be piloted to crash onto a target and most could be fitted with an improvised explosive warhead. However the primary use of a UAV or UCAV would be for recoverable flight operations carrying reconnaissance equipment and/or munitions. While many UAVs are explicitly designed with loitering in mind, they are not optimized for a diving attack, often lacking forward facing cameras, lacking in control response-speed which is unneeded in regular UAV flight, and are noisy when diving, potentially providing warning to the target. UAV's, being designed as multi-use platforms, often have a unit cost that is not appropriate for regular one-time expendable mission use.

The primary mission of a loitering munition is reaching the suspected target area, target acquisition during a loitering phase, followed by a self-destructive strike, and the munition is optimized in this regard in terms of characteristics (e.g. very short engine lifetime, silence in strike phase, speed of strike dive, optimization toward loitering time instead of range/speed) and unit cost (appropriate for a one-off strike mission).

Ethical and international humanitarian law concerns: Loitering munitions that are capable of making autonomous attack decisions (man out of the loop) raise moral, ethical, and international humanitarian law concerns because a human being is not involved in making the actual decision to attack and potentially kill humans, as is the case with fire-and-forget missiles in common use since the 1960s. Whereas some guided munitions may lock-on after launch or may be sensor fuzed, their flight time is typically limited and a human launches them at an area where enemy activity is strongly suspected, as is the case with modern fire-and-forget missiles and airstrike planning. An autonomous loitering munition, on the other hand, may be launched at an area where enemy activity is only probable, and loiter searching autonomously for targets for potentially hours following the initial launch decision, though it may be able to request final authorization for an attack from a human. The IAI Harpy and IAI Harop are frequently cited in the relevant literature as they set a precedent for an aerial system (though not necessarily a precedent when comparing to a modern naval mine) in terms of length and quality of autonomous function, in relation to a cruise missile for example.

List of users and producers: As of 2023, loitering munitions are used by the armed forces of several countries, including:

 Argentina – HERO 30, HERO 120
 Armenia – HRESH, BEEB 1800, AW21
 Australia – Drone 40, Innovaero OWL
 Azerbaijan – IAI Harpy, IAI Harop, Orbiter 1K, SkyStriker, STM Kargu, Qirği, Quzgün
 Belarus – UBAK-25 Chekan
 Brazil – Anshar
 China – IAI Harpy, CH-901, WS-43, ASN-301
 France - Switchblade, Colibri, Larinae
 Georgia - Delta-WB Warmate
 Greece – Attalus, Aihmi AHM-1X
 Indonesia – Rajata
 India – Nagastra-1, IAI Harpy, IAI Harop, SkyStriker, Warmate, Trinetra, ALS-50, Johnnette JM-1, Shaurya-1, Kadet Loitering Aerial Munition, Overwatch PHOLOS
 Iran – Karrar, Shahed 131, Shahed 136 (loitering capabilities disputed), Hesa Ababil-2, Raad 85, Arash-2, Meraj-521, Meraj-532, Zhubin, Shahin-1, Shahed 238 and possibly others
 Israel – IAI Harpy, IAI Harop, IAI Harpy NG, IAI Green Dragon, IAI Rotem L, Orbiter 1K, Delilah, SkyStriker, Spike Firefly, HERO loitering munitions series, Viper, Lanius, Point Blank, SpyX, and upgraded variants.
 Lithuania – Switchblade
 Morocco – IAI Harop
 Poland – WB Electronics Warmate
 Portugal – UAVision Elanus
 Russia – ZALA Kub-BLA ("Cube"), ZALA Lancet, Geran-1, Geran-2
 Serbia – Gavran, Osica, Komarac, Vila 1
 Singapore – IAI Harop
 Slovakia – AX-2 Predator
 South Africa – Paramount N-Raven
 South Korea – Devil Killer, IAI Harpy
 Spain - Q-SLAM-40
 Sudan – Kamin-25
 Taiwan – NCSIST Chien Hsiang, NCSIST Fire Cardinal
 Turkey Robit UAV AZAB, – IAI Harpy, STM Kargu,  STM Alpagu, Transvaro-Havelsan Fedai, LENTATEK Kargı, Roketsan-STM Alpagut
 Turkmenistan – SkyStriker
 UAE – QX-1, Hunter SP, Hunter 2-S, Hunter 5, Hunter 10, Shadow 25, Shadow 50, RW-24, N-Raven
 United Kingdom – Switchblade, Overwatch PHOLOS
 United States – ALTIUS-600M, AeroVironment Switchblade, Phoenix Ghost, Raytheon Coyote, HERO 120, Point Blank.
 Ukraine – RAM II, Switchblade, ST-35 Silent Thunder, Phoenix Ghost, Warmate, Bober, AQ-400 Scythe, UJ-25 Skyline, Overwatch PHOLOS, QinetiQ Banshee, ALTIUS-600M
 Yemen – (Houthis) – Qasef-1/2K, Shahed 131, Shahed 136, Samad-2/3, Shahed-101

See also: Boeing Persistent Munition Technology Demonstrator
Flying bomb
Low Cost Autonomous Attack System
Sypaq Corvo Precision Payload Delivery System
Television guidance
V-1 flying bomb
XM501 Non-Line-of-Sight Launch System

References: 

External links:  Media related to Loitering munition at Wikimedia Commons