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 ...
EDN

An open, scriptable USB interface for host driven electronic experiments

SigLab is a combination of open hardware and FOSS (free and open source software) projects to provide easy to use and full featured scriptable USB interface for digital electronic experiments. SigLab ...