What is the meaning of `ppa:x/y`

I know how to add a PPA to Ubuntu. But I don't know what this ppa:x/y PPA format means!

For instance :

# (VLC PPA)
sudo add-apt-repository -y ppa:videolan/stable-daily

What is videolan and what is stable-daily ?

This is the format:

ppa:user/ppa-name

In your case:

ppa:videolan/stable-daily

• videolan is the user name. You can open http://launchpad.net/~videolan to see its page
• stable-daily is the package archive name

This user has two package archives:

In ppa:X/Y the value X is the user name of the PPA's owner at launchpad.net, and Y is the name of the PPA.

The PPA's web page is always at

https://launchpad.net/~X/+archive/Y

and the package archive is at

http://ppa.launchpad.net/X/Y/ubuntu

For example for

 ppa:videolan/stable-daily 

the web page is

https://launchpad.net/~videolan/+archive/stable-daily

and the package archive is

http://ppa.launchpad.net/videolan/stable-daily/ubuntu