What is I2C communication protocol?

I2C (Inter-Integrated Circuit) is a synchronous serial bus using two wires: SCL (clock) and SDA (bidirectional data). Multiple masters and slaves share the bus with each device having a unique 7-bit address. Communication involves: Start condition, slave address + R/W bit, ACK, data bytes with ACKs, and Stop condition. Features include: Multi-master support, built-in addressing, acknowledge mechanism, and clock stretching. Standard mode is 100kHz, Fast mode is 400kHz. Used for sensors, RTCs, EEPROMs, and low-speed peripherals.