As you enter into this hobby, one thing you'll notice is that most things come in the form of acronyms. For example: how do I hook up my VTX to my AIO FC so my FPV feed with OSD comes through? If you dont know these acronyms, then this entire question was nonsense to you, so let me try to explain...
This is probably the most fundamental of all of the acronyms, and simply stands for flight controller. This is different from what you may think fo the controller (the transmitter or 'remote'). The flight controller is actually the 'brain' of the drone, containing the processor gyro, accelerometer etc. You get the idea. It's important to know the difference between a controller (read transmitter) and a flight controller.
The ESC is the electronic speed controller, and this is what translates signals from your flight controller into signals that are usable by the motors. The ESC also provides power to the motors from the battery. You need one ESC per motor, or you can get a 4-in-1 esc for a quadcopter that combines all of the ESCs into one, and also acts as a PDB (see below).
One of the most commonly used acronyms in the drone racing and freestyle world, FPV simply stands for First Person View. This is done in a few ways, either by goggles, which are the most common choice, or by a separate monitor or even wrist-mounted screen. Toy-grade quads, such as the Syma X5SW also have FPV of a different kind, which is transmitted over WiFi instead of the low-latency analogue 5.8GHz video transmissions of racers and freestyle quads.
OSD stands for On Screen display, and it comes in two forms: the most commonly referred to OSD is overlayed by the FC into the video feed and contains flight metrics such as the RSSI, battery voltage, GPS if installed etc. The other type of OSD is the OSD that is incorporated into the FPV receiver system that shows you (and can allow you to change) the status of your FPV receiver/screen setup, like how much battery you have left, what channel you are receiving, what you contrast settings are etc.
LOS/VLOS stands for line-of-sight and/or visual line-of-sight. This means that you can see your aircraft when you are flying it, and many places have laws that state your drone must be within LOS of either yourself or your spotter when you're flying. Always make sure to check your local laws before flying to make sure you know the regulations regarding LOS.
PDB stands for power distribution board. For setups that don't have a 4-in-1 ESC, you will need a separate PDB to provide powe to the FC and ESCs from the battery. In my experience, these seem to be used less frequently on newer builds in favour of a 4-in-1 ESC to save space and give a (subjectively) cleaner looking build.
TX stands for transmitter, and this is what you hold in your hands to control the aircraft. Some people tend to call this the controller, but this can easily be confused with the flight controller, so I tend to stick to saying either transmitter or radio. You also don't want to get this confused with your VTX (see below).
RX stands for receiver, and picks up the signals that are sent by your transmitter. Some recievers may offer diversity, telemetry, auto-binding and differences in range. Some may also be smaller than others and so fit better in your build. Make sure your receiver is compattible with your transmitter, and if it is a FrSKY product, make sure they are on the same version and region settings.
The VTX, or video transmitter, is what sends the signal to your FPV goggles or monitor. It's usually hooked up to your camera and flight controller, but in cases such as Tiny Whoops, where you need to save as much space as possible, you can get an AIO (all in one) camera and VTX combo that just plugs into the flight contoller for power and, if available, OSD. These most commonly transmit on the 5.8GHz spectrum for FPV.
Like the RX, the VRX is a reciever, but for the signal from the VTX. You probably won't hear this term used too often - usually it's just called a module or ground station (depending on the type of VRX you have).
An SMA connector is a type of connector that is used with coax cable, which means it is very commonly used in the FPV world on both video transmitters and receivers. SMA connectors have a scre thread, which means they are easy to install and very durable, however that does come at the cost of a small amount of extra weight, which may mean that if you're looking to squeeze as much speed as possoble out of your quad, this may not be the kind of connector you want to go for.
RP-SMA is just like SMA, except the RP stands for reversed polarity. This does have physical implications on the actual connector, but it is just a different kind of SMA. RP-SMA won't work with an SMA connector, unless you use an adapter.
This is another kind of connector that is mainly used with a VTX, not a video receiver. This is becase whilst they are very light-weight (so good for squeezing extra speed out of a build), they are really not that durable, and are only rated for in the tens of mating cycles. U.FL is (in my experience) becoming less popular in the drone world in favour of MMCX (see below).
MMCX is kind of the mid-point between IPEX and SMA - it is still light-weight, whilst being much more robust than an IPEX conector. This type of connector is still not being used on goggles, ground stations or monitors (at least not commonly), however, as SMA is still easier and more robust.
If you fly racing or freestyle drones, you will most likely have heard of (and use) acro mode. In this mode, the drone doesn't self level - instead, it will stay in whatever orientation (attitude) you put it. This means that letting go of the sticks doesn't make the quad go into a 'level' or hover position; if you are going forwards, you will continue to go forwards, if you are going sideways... well, you get the idea. This is kind of the way most racing and freestyle pilots fly (except most of us fly with airmode on) because it means you can do flips, rolls, powerloops etc. and don't have to fight the drone to have complete control.
Airmode is an addition to whatever mode you fly in, and it means that even when your throttle is at its zero position, your motors are still idling. This is useful because it means that you still have control of the quad, even at zero throttle, adn gives you extra authority going into tricks. Imagine you're going into a Matty-flip, but you need to bail out when you're still upside down. Without airode on, you'd have to raise the throttle to give you attitude control, taking extra time and risking launching yourself into the ground if you apply too much throttle. With airmode on, you just roll out of the stunt. Simple!
This is how lots of people start flying, and how all stabilised camera platforms (that I know of) operate. In this mode, as soon as you release your pitch/roll stick (if you fly a mode 2 transmitter, as most pilots do, this is the right stick) the drone will level itself and do its best to remain level, basically trying to hover. This mode also limits the maximum pitch/roll angle, so you can't do manual tricks (unless you have artes so high and such a great momentum that pitching or rolling sharply will cause your quad to lose stability. If this is how yo are trying to do tricks, it's probably worth you giving acro mode a go.
Horizon mode is kind of a hybrid between acro and angle mode. When you're flying horizon mode, the drone will act like it's in angle mode when you aren't giving any stick inputs, but it doesn't have an angle limiter on it so you can still do tricks.
This mode means that no matter what orientation the drone is in (what way it's facing), backwards is always towards you and forwards is always away from you. IOC stands for 'intellignet orientation control'. Personally, I dislike flying this mode. I've been flying either acro or angle for a long time, and headless mode just adds extra confusion, and makes flying FPV pretty much impossible.
Return-to-home/return-to-base just means the drone flies back to you automatically. On higher end drones, this is done using GPS. on toy-grade drones, this is done by switching the drone into headless mode and pitching back (this isn't really a reliable method of RTH as if the gyroscope drifts, the drone has no real way to know what direction 'home' is).
Flying via waypoints means you let the drone fly by itself and provide it with a set of coordinates that it needs to pass through. This is achieved through GPS, and so doesn't really apply that often to racing and freestyle pilots, but is very useful for fixed-wing and camera-rig pilots.
If you fly a DJI drone, you will probably be familiar with ATTI mode. ATTI mode just stands for 'attitude mode', and in this mode, the GPS is disengaged and you are given manual control. This means the drone will just fly in regular angle mode without geofence and GPS hover.
As the name suggests, this is the mode in which the drone will follow you, either by giving you a separate GPS tracker, following the remote or, as more modern drones are starting to do, using the camera to identify the target and follow whatever it is (animals, vehicles, people etc.)