I've just received the information that I earned the Android Badge - anyway I couldn't find this badge in the listing. Is there a description available on how this badge is earned and are there more badges which are not described in the badges list?
It's a tag badge. The full list is here. This lists the requirements for each level of the badge (bronze, silver and gold). You need to get a total score above a threshold and provide a certain number of non-community wiki answers to earn the badge.
The android badge lists all the recipients. Your name is first (at the moment) as you are the latest recipient.