Microcontroller
MCU, e.g. Arduino Uno's ATmega328P, ESP32
A microcontroller is a tiny computer on one chip that reads sensors and controls things using a program you write.
Arduino boards make one easy to program over USB. The ESP32 adds Wi-Fi and Bluetooth.
Words to know
Everything on this subject: Microcontroller Basics: Pins, PWM and Signals, Simplified