Kayla, it’s liquid. Fermented milk. You’ll find it in the refrigerated section of the grocery with the yogurt. The most common brand is LifeWay. Get Plain, unflavored (no sugar), and full fat is fine. 🙂
Kefir made from goat milk is even better, though pricier. I alternate between the two.
Even cheaper is to make it yourself. It sounds odd, but you put the kefir kernels in milk and leave it out. Most people I know who’ve tried this have more kefir than they know what to do with!
Blog on how to make kefir
http://www.thekitchn.com/how-to-make-milk-kefir-cooking-lessons-from-the-kitchn-202022
