I came here just to write this... As the co-founder of Arduino I find this use of Arduino as a generic "microcontroller board" or "not a raspberry pi" a bit shocking.. :)
If it's any consolation, everyone seems to feel the need to invent a new word for daughterboard for their own flavor of microcontroller / single board computer.
Isn’t Arduino both a hardware term and a software term? I’m working with a nRF52840 board, but I’m using the Arduino IDE to author Arduino code to run on it.