Glossary
UART
UART is a simple serial link, often left on circuit boards for debugging, that sometimes gives access to a console.
UART (Universal Asynchronous Receiver-Transmitter) is a very simple serial link: two data wires (TX to send, RX to receive) and a shared ground (GND), with no shared clock.
Many circuit boards keep a UART port for debugging. Connected to a USB-serial adapter, it often prints boot messages, sometimes a console. It's one of the first entry points studied in hardware hacking, on your own devices.
Mind the voltage: 3.3 V and 5 V don't mix, and you never connect the power pin (VCC). A logic analyzer helps identify the pins and the baud rate.