I wanted to write a short primer on missile terminology at the start of the week, but my phone deleted most of it so I ran out of energy. Here it is again.

#Aerodynamics: Hypersonic: Technically a buzzword, but is regarded at Mach 5 (aka 5x the speed of sound). In US Military terms, this refers to a weapon that can perform maneuvers at this speed above. Ballistic missiles travel at above hypersonic speeds or above by virtue of all their other properties, but don't fill the US military definition as they don't do maneuvers in response to incoming fire. Even the original V2 approached hypersonic speeds. This speed makes the weapon difficult to intercept, as there's less time to intercept and any change in direction is "larger" for the purposes of interception. However, most cruise missiles and anti-tank missiles are not hypersonic, and are even subsonic. Hypersonic velocities introduce some aerodynamic and physical/mechanical complications that slowly increase depending on the local air pressure and multiple of the speed of sound. As a counter-example, a Mach 10 projectile 60 km above the Earth's surface will not produce the same plasma envelope or heat as the same profile projectile 2 km above the Earth's surface. Be wary when seeing this term in the media, it sometimes refers to ballistic missiles, which is nothing special unless they can course correct.

Supersonic: An actual technical term that means above the speed of sound in a given context. You know this. At sea level (and for many military applications), this is roughly 340 meters a second (1200 kmph or 760 mph). There are a bunch of aerodynamic qualities that change around this speed. I say around as air flowing past a bit sticking out (say, a wing, or radio antenna etc) will cause air to flow faster than the speed of sound, creating lateral forces that affect the vehicle (vehicle: plane, missile, bullet etc). Those lateral forces mean a vehicle will want to be solidly above or below the supersonic threshold. The lower the air pressure (usually, the further up) reduces the speed of sound, but also reduces the supersonic effects (to zero, as you slowly go up into the stratosphere). For long ranged air-lining, a higher altitude where your jet engines still run is better, but for other purposes it varies a lot.

Subsonic: Slower than the speed of sound. You are this, probably.

Missile Types: Ballistic Missile: A vehicle (plane, missile, or bullet) that follows approximately a ballistic trajectory. Usually, such a vehicle will expend all of its fuel on the way up (at most), and rely on orbital mechanics to maintain its speed on the way down. Longer ranged ones will avoid the Earth's atmosphere for a lot of the journey. This means that such a vehicle will be very speed<->weight/fuel efficient. If it isn't striking a moving target, it also needs the least amount of redirection by weight. Its main disadvantages are that its very easy to detect by RADAR, since it by definition goes over the horizon very far away, and that it can get difficult to course correct for many reasons. As the air pressure goes down due to altitude, your aerodynamic surfaces matter less. As the pressure and speed increase, both heat and RADAR are less effective on the way down. Nonetheless, they are very hard to shoot down. Famous examples: V2 Rocket, Iskander, Kinzhal, and ATACMs. They're also cheaper per range/weight.

Cruise Missile: A missile that follows the curvature of the Earth (instead of ballistic trajectory), usually powered by a jet Engine and are usually subsonic. Compared to Ballistic missiles, they're easier to guide and harder to detect by RADAR. However, once they are detected, they are easier to shoot down. They can even be chased and engaged with fighter aircraft. Some of them have a lower powered RADAR that lets them follow terrain up and down, making their visibility extremely low when going cross-country. Cruise missiles have an ascending, descending, and a cruise trajectory, and generally behave like a plane (indeed, the original Kamikazes planes were called early cruise missiles, but the V1 is closer to what we'd call a cruise missile). They have similar vulnerabilities to planes. Various methods of making them harder to shoot down, coating them in RADAR absorbing paint, making them faster during one stage (often descent, for things like the Zircon), RADAR following terrain, Jinking maneuvers on descent, hardened noses etc. Famous examples include the V1 Buzz-bomb, Tomahawk Missile, Zircon... Anti-ship missiles are often a variation of this, flying lower and with less range but otherwise performing the same function.

Missile: Much talk of missiles, traditionally it means something that isn't powered in flight (e.g. an arrow, rock, bullet etc), but nowadays means an unmanned powered flight weapon (e.g. a cruise missile, ballistic missile etc). Nonetheless, it is always separated from the operator and firing mechanism, as is tradition.

Anti-Aircraft Missile: The Ballistic and Cruise Missiles usually go to destroy battlefield assets of one sort or another. AA missiles specifically destroy missiles and aircraft. They tend to be the fastest rocket powered missiles for their size. Things like the Patriot or the S-500 are AA missiles, and are capable of catching up to and destroying other missiles even if the other missile has passed the launch point. The tend to fly in a straight-ish line, always heading for the predicted trajectory of the target.

Drone: Often powered by an electric motor, subsonic, and intended to loiter in the battle space until needed, as opposed to launched for mission. Blurry term.

Motors:

Rockets: Rockets are high power per weight, high power per time, and extremely cheap. Their disadvantages are running time and they are less able to be controlled (there are fuel rockets, but that's generally outside the scope of a military context). They are mostly used on Ballistic and AA missiles, and the final portion of some cruise missiles. The smallest missiles (MANPADS, MANPAT?, etc) also tend to use rockets for their simplicity, tolerance to size, and cheapness.

Jet Engines: Jet Engines offer very high power to weight ratio, weight to range, and medium efficiency. They're usually found on cruise missiles and aircraft. Some cruise missiles final stage may seem like they attain rocket-like velocities, but in-fact use scramjets to attain this velocity. They tend to be very high cost for all dimensions (range, efficiency, volume etc), but fulfill a niche in between traditional combustion engines and rockets.

Piston Engines: Outside the scope of missiles and aircraft nowadays, though they used to be used in aircraft. They are cheap, have high tolerances and fuel efficiency, and can adjust their power for a purpose very well. They tend to be quite heavy for their power output though. Poor torque at low RPS compared to all other engine types. We don't see these on missiles or aircraft atm and I don't see it except in some extremely niche cases.

Electric Motors: These tend to be somewhere around Jets and Pistons, though they tend to have quite high weights to volume and power. They offer very high torque at low RPS compared to jets and lots of power variability, and much lower mechanical complexity compared to equivalent Jet and Piston designs. As the line between missile and drone gets blurred, I imagine we'll see this blurred. However, for the time being, if something is electrically powered and seems like a missile, it is a "drone".

Motor vs Engine: Motor provides motive force generally, engine provides motive force with internal combustion. Colloquially, these are pretty interchangeable. However, if you need to... Steam Engine, Jet Engine, Electric Motor, Pressure Motor. Usually, this is rotary. Rocket engines, despite being a combustion system, often get called motors.

Guidance systems:

RADAR: The standard method of tracking aerial targets and sea targets. Metal reflects Radio very well compared to air or water, or even soil, so this can be tracked very easily. Sometimes, especially for smaller projectiles (e.g. AA guns), the RADAR is on the ground and the projectiles pull into the reflection from the target until they are close enough. Missiles can also track into such a reflection; Semi-homing RADAR (Fox-1). For larger systems, a RADAR array can be mounted on the projectile (active homing RADAR, Fox 3). This is used in civil and military aviation constantly, but can also be used for reversing your car, speed detectors etc. Can be jammed, but not as easily as you'd think.

Infrared/thermal/heat-seeking: (Fox 2) The main method other than RADAR for tracking aerial targets. Aircraft tend to run hot. Thus, an infrared camera can track a projectile into a target for much cheaper. Most military aircraft carry flares to guide heat-seeking projectiles away, to varying degrees of success. This also tends to be pretty short ranged; infra-red gets soaked up by the atmosphere pretty quickly. Also, for faster missiles, the nose cone gets hotter as the velocity increases, which reduces the ability of thermal optics to see any target.

Manual or external guidance: Receiving data from somewhere else to guide the missile. Wire-guiding on anti-tank weapons is a classic method of this, however the modern Dong Feng uses transmissions from an AWACS to guide to target. These tend to vary quite wildly and their counter-systems also.

Aerodynamic Control: Uses fins and wings to control the direction of movement. Only applicable for low altitude missiles, and less applicable for supersonic vehicles (but not inapplicable, you just have to design around it)

Gyroscopic Control: Stabilisation control that allows you to adjust heading based on previous velocity. Used in conjuction with other controls.

Vectored Thrust Control: Uses thrust from the Motors to control the direction of movement. The only valid method of control when outside the atmosphere.