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

What's the technical name of a motherboard USB header connector?

The USB A female connectors were easy to find on Digi-Key's website. However I'm not sure what the technical name is for the motherboard header for USB. Anybody know? Or alternatively, anyone have a ...
Ars Technica

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

This one is a powered hub (using a SATA connector) going to a standard USB 3.0 header. My assumption is that it functions like a 4-port hub connected to a single set of pins coming from the header (so ...