Betaflight isn't an acroym really it's "just" a piece of software/code that reads sensors on and it runs on the micro-controller [MCU] (stored in memory and executed by processor in there). There is also a windows/mac/linux compatible "Betaflight configurator" which you can use to connect to and modify the configuration of any "betaflight compatible" flight controller. The "configurator" program can also download and "flash" or update your MCU with new versions of betaflight as developers make updates.
Betaflight is an open source project so basically anyone can look at the source and offer contributions and certain people who "own" or created the repository of code retain rights to allow or deny any code from getting in. Basically they will review it and make sure it is up to snuff and shouldn't break anything, then they do extensive testing with their own gear and then roll it out to the community (this process changes over time for different open source projects).
Cross platform configuration tool for the Betaflight firmware - betaflight/betaflight-configurator
github.com
https://github.com/betaflight/betaflight-configurator/releases <-- scroll down to "assets" to see the installers for different OSes for betaflight
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Acronym soup is an easy way to get lost, for the uninitiated to the build it yourself from scratch "scene":
TX = Transmitter (generic term sometimes refers to the controller/transmitter in your hands that sends control signals sometimes refers to a wire sending data out from one board to another board so they can control each other or otherwise communicate)
VTX = Video Transmitter - it takes in an analog video signal from a basic analog camera and converts that video signal into radio waves so they can be transmitted out of an antenna and then received by a ground video receiver (usually the video receiver is built in or added as a module to goggles)
FC = Flight Controller it is the "brain" of the quadcopter, physically it is a printed circuit board (PCB) with an integrated processor on there called a micro-control unit (MCU). The MCU stores the program that runs to fly your quadcopter that reads inputs from a control receiver and sensors and sends control signals to electronic speed controllers (ESCs) which in turn control the speed of each motor to keep the thing level.
Another way to say that is the FC is the flight computer that does all the actual flying (keeping thing level or responding to your control input)
FPV = First person view, flying with goggles or a screen where you see from the perspective of the camera on the drone, the camera video signal is hooked up via a wire to the VTX ultimately and transmits the video signal to the pilot on the ground
LOS = line of sight, flying without goggles/screen, no VTX or camera even necessarily required any off the shelf toy quad can do this
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