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

Can you attach multiple USB-C plugs to a single motherboard header?

I've got a motherboard that has a single USB-C header on it. I also have a case with no USB-C ports on the front panel. I know things like this exist, but I'm wondering is, is there anything with ...
Ars Technica

Not enough motherboard USB headers

Hello all.<BR>First post -I did use the 'Find' option but didn't see an answer.<BR><BR>I am installing a card reader on the front of my PC and it needs to connect to the headers of the motherboard.