I2C and SPI are two peripheral busses

Both are synchronous serial lines
Synchronous means that the clock is delivered with the signal
The serial port it _a_synchronous
UART = Universal Asynchronous Receiver Transmitter

They replaced the "textbook" legacy data bus / address bus
Such interfaces are complex to manage, and requires many tracks
Nowadays they are only used for RAM, and little else

Another interesting bus is "OneWire", that we won't cover today

A simple summary, that encompasses everything:
UART (RS232) is two wires, asynchronous, point to point.
I2C is two wires, one master and slaves
SPI is three wires + enable, one master and slaves
OneWire is one wire (+ GND), one master and slaves