What is Amazon.com gift sertificate

I have not worked with Mturk. But from my knowledge, an amazon gift certificate is just like any other store certificate in this case specifically for Amazon.com. This certificate will allow you to purchase anything you please from amazon, within the limit that the certificate amount indicates. So simply, its a certificate that indicates a certain amount of money, which you can only use on amazon's site. Though you are limited to only amazon's site, they do have a large selection of items, very similar to ebay.

I haven't worked with Mturk, but I am familiar with these certificates anyway. It basically means you can buy whatever you want with them on Amazon. And since Amazon sells almost everything, it is a pretty good thing to get, I think! (I would just make sure they ship to your country first. There is a possibility they don't ship everywhere, I guess)