The name has already been taken

[matanui159]

This is just a quick question. I'm adding my first modpack, being called MataPack, and I'm getting the error:

The name has already been taken.
The modpack name you entered has a slug that already exists.

I understand the first half (although I am surprised, I thought the name was pretty unique), but what does the second half mean? I already had a look around on the internet but couldn't find anything.

Thanks in advance.

Edited January 23, 2016 by matanui159