[szszrk]

The nexus part was laid out nicely by others. ntlm proxy is a proxy that can authenticate inside a corporate network with your own credentials and forward all requests, while exposing a simple old school proxy. You hit simple local proxy, it gets forwarded to a small tool that does NTLM auth inside your company's network pretending you are doing that traffic yourself.

This is hopefully a trend that is disappearing with a wave of modern transparent proxy solutions, but in general companies tend to set up proxies that get automatically authorized by your workstation. It may have some issues with less known browsers and your console tools will not be able to use that at all.

So when you build something locally, want to download a .deb, or a pypi package to have modern Python tools your are out of luck - you have to download it manually using a browser or not at all.

This is where such proxy comes into play.