The name is kind of weird.
It is the process of when you take a cartridge converter pen and just get rid of the converter or cartridge and fill the whole body with ink.
Not all pens work well for this. First of all the body should be plastic and you should test that it is tight. I personally think that clear or kind of clear materials are better for this. Mostly because it is so cool looking at all that ink moving around inside the pen.
Everything you need to do this is a synringe to fill the body and some silicone grease to use on the threads where you screw the body and ink section together to keep ink from leaking.
With the right pen this looks so awesome. With my Pocket 66 I sometimes sit there fliping the pen looking the ink splash around.