It's a shell command that allows you to `cd` to places without having to type the whole path. Some implementations are https://github.com/wting/autojump and https://github.com/rupa/z.

A very simplified example: if you call `j pro`, the command should take you to the folder that best matches the name based on some criteria (in my case, one of them would be frecency). In my case, that would be my projects folder in another drive.

The nifty thing about them is that you don't have to make those aliases manually -- the tool learns the directories you've visited over time.

Of course, the tool could take you to the wrong path, but with a well made set of matching/prioritization rules, I've found it more useful than not.