What is a USB 'header' (and how is it different from a port)?

With the prevalence of USB devices, it might be easy to mix up USB headers and ports, but there is a key difference between ...
Ars Technica

Motherboard Or Case?

I accidentally plugged a USB c cable into one of the front case USB a 2.0 ports. The computer did not shutdown, the computer cases two front USB 2.0 ports stopped working (my Logitech receiver is ...