'Serial USB Terminal' is a terminal / console app for microcontrollers arduinos and other devices with a serial / UART interface connected with a USB to serial converter to your android device.

This app supports USB to serial converters based on
- FTDI FT232 FT2232 ...
- Prolific PL2303
- Silabs CP2102 CP2105 ...
- Qinheng CH340
and devices implementing the USB CDC protocol like
- Arduino using ATmega32U4
- Digispark using V-USB software USB
- BBC micro:bit using ARM mbed DAPLink firmware

To connect USB to serial converters your android device must support USB OTG aka. USB host mode. Most devices support this today but please check with one of the various USB test apps if host mode is enabled in your android kernel.