They are small sections of video saved as gifs so they can be made to look really like moving pictures.
You can see a lot of really impressive cinemagraphs here.
I've had a go myself and here are the results. Please let me know what you think.
Above: Hot chocolate from Angelina Bakery.
The next one is a bit heavy so see it after the jump.
This is more of a gif than a cinemagraph because I didn't mask anything off. And I couldn't make it loop because it's all moving! But I still think it's pretty and sparkly!