What does that do, add already tracked files only?
It interactively shows you each change that would be added and lets you decide whether it should be staged or not. Down to the hunk level, so you can partially stage a file if you so choose.
Oh, that's neat.
The -p presumably stands for pInteractive with a silent p :)
Ha! It’s actually patch (as in select parts of the patch) though I remember it as partial.
There's -i for interactive, lets you add, patch and reset (unstage).