Arduino for STM32

Does dfu pertain to the microcontroller settings on Arduino IDE? Or is that a software that is already uploaded on the computer?

We are doing a senior design project that involves uploading Arduino code to a Adafruit Feather STM32F405 Express. Everytime we try to upload it, we are met with an exit status 127 or an exit status 1. We follow the preferences/tools on the Adafruit website: https://learn.adafruit.com/adafruit-stm32...