The offer is by 1&1 internet inc and they are offering you a one year .biz domain.This is a limited time offer so you have to hurry as they have not given the deadline of the offer so people are going to be rushing for those domains.By the way .biz domains are only for businesses and commercial use so make sure your website complies with the above before you sign up.
Here is the link to follow to get the free domain.1and1
