Different interfaces of microcontrollers and peripheral devices.
Universal Asynchronous Receiver-Transmitter (UART) is an asynchronous serial communication interface.
Inter-Integrated-Circuit (I2C) is a synchronous, multi-master, multi-slave serial communication bus. It uses two bidirectional open collector or open drain lines with pull-up resistors.
Serial-Peripheral-Interface (SPI) is a synchronous serial communication interface.
1-Wire is a bus system (data rate 16.3 kbit/s) designed by Dallas Semiconductor (now Maxim Integrated).
Musical Instrument Digital Interface (MIDI) is a communication protocol/standard for musical instruments.