The WHOIS Data Reminder Policy (or WDRP) is an ICANN policy which requires domain registrars to contact you once a year and remind you to update your contact information. This means you will get an email once a year for each domain you own requesting that you make sure your information is up to date.
In the WDRP email from Gandi is a special link which allows you to view what information is on file for your domain. This link is available only to you and allows you to see information that may be otherwise blocked in the WHOIS database for privacy reasons. This link is valid for two weeks after you receive it.
If you need to update your information you can read how to in the other pages in our section on changing account information.