USB-C (formally USB Type-C) is a connector shape, not a speed standard by itself. It is reversible (no wrong-way-up), physically small, and can carry power, data, and even a video signal (DisplayPort/Thunderbolt Alt Mode) over the same cable.
On a refurbished laptop, USB-C is a good sign of a more modern machine, and often means you can charge the laptop with the same cable/charger you use for many phones and tablets.