Your "product key" is always permanent. Just be sure you do not share it with other people.
To find your current license:
- Click Help > About Visual Studio
- Along the top there is a hyperlink -- "Product license information". Click that.
It will show you your current license.
For a quick and layman understanding of Visual Studio licensing, you can check this blog:
http://www.colinbowern.com/posts/visual-studio-licensing-in-a-nutshell
Cheers!