1: What is a "Google Adsense link" ?
2: Why do you want to hide a link like that for ? What is the reasoning behind it ?

Adsense is the link that's on someone's website to earn revenue. Usually, when you have an adsense link on your site it shows the link, description of the link and the URL where the link will take you.

However, I've seen several websites that only have the top-level link and the description and destination address is missing. You can see an example of what I'm talking about at the securityguardtraininghq website.

Those are link units.

[support.google.com...]

lame wolf is rite, however I found out that link units perform usually pretty bad on my sites.