MCU - Microcontroller Unit (Main processor chip of FCB eg. STM32F405)
IMU - Inertial Measurement Unit (Gyro and Accelerometer chip eg. MPU 6000)
Baro - Barometer Altitude sensor (eg. BMP280)
Magnetometer - Electronic Compass (eg QMC5883)
DFU - Direct Firmware Upload (Processor Mode which allows firmware upload)
MSP - Multiwii Serial Protocol. Communication protocol used by INAV and FCBs. MSP came from Multiwii software, which was derived from the Nintendo Wii Game Controller.
Serial Port - Pins or pads on FCBs for connecting external devices. Serial means all channel signals use the same wire.
UART - Universal Asynchronous Receiver Transmitter Serial port. Pins or pads where UART devices (GPS, RC receivers, camera controls) connect to the FCB. Pins labelled - Ground Voltage RX TX. RX from the device connects to TX on the FCB
I2C or I squared C - Inter Integrated Circuit Serial port. Pins or pads where I2C devices (compass, OLED screen) connect to the FCB. Pins labelled - Ground Voltage SDA SCL
SPI - Serial Peripheral Interface. Connection interface for onboard devices like SD card reader and barometer
ADC - Analog to Digital converter. FCB component that converts a varying voltage input to a digital output. Used for displaying battery voltage, current, analog airspeed sensor and analog RSSI values.
Soft Serial - Extra Serial port enabled in software, by repurposing spare UARTs pins. Eg Smart Port telemetry connection to an unused TX pin.
Vbat - Flight battery Voltage. May be filtered on some FCBs to reduce video interference
OSD - On Screen Display
GNSS - Global Navigation Satellite System (Commonly called GPS, but GPS only refers to the US satellite system. Other GNSS systems include Galileo, GLONASS)
OLED - Organic Light Emitting Diode used in OLED data display screens and some FPV goggles
RSSI - Received Signal Strength Indicator. A number representing the strength of an RC signal at the receiver.
LQ - Link Quality. A number representing the strength and quality of an RC signal.
LFR - Lost Frame Rate % - Percentage of lost frames in an RC Signal
PWM - Pulse Width Modulation. Basic RC signal protocol which uses an individual wire for each channel signal. Used for connecting servos to a receiver or receiver to FCB.
PPM or CPPM - Pulse Position Modulation. Serial RC protocol. Used for connecting a receiver to FCB, or RF module to a transmitter. All channel signals on one wire
SBUS - FrSKY and Futaba Serial RC protocol. Used for connecting a receiver to FCB, or RF module to a transmitter. All channel signals on one wire.
S-Port - FrSKY Smart Port Telemetry system. Extra socket found on FrSky receivers to connect telemetry sensors.
F-Port - FrSKY SBUS and SPort combined. RC and telemetry signals on one wire.
F-Bus - F-Port version 2
Tandem (TD) - FrSKY RC system which uses 2.4GHz and 900MHz RF simultaneously
iBUS - FlySKY Serial RC protocol. All channel signals on one wire.
CRSF - Crossfire. Team Black Sheep long range RC protocol. Similar to FPort.
R9 - FrSKY Long range RC 900MHz protocol
ExpressLRS (ELRS) - Open Source, Long range, low latency RC system. 2.4GHz or 900MHz versions. Uses the CRSF protocol.
ESC - Electronic Speed Controller
BEC - Battery eliminator circuit. Confusing term for a voltage regulator found on ESCs and FCBs. BECs reduce and smooth out the battery voltage for use by lower voltage devices. Eg. 9V or 5V for FPV gear, 5, 6 or 7.2V for servos.