Gari (がり) is pickled ginger. Pickling is a popular cooking method in Japanese cuisine, called tsukemono. (漬物, つけもの) Gari is the pink shaved stuff commonly served with sushi. It can be found in a plastic jars, and if your grocery store has sushi in the deli, they might have it on the shelves as well.
Ginger acts as a preservative, which is why it is often packed with rice: it helps keep it fresh! It also has antiseptic properties, which is another reason it goes with sushi: it traditionally helped counter the ill effects of bad fish, but with food preparation standards today, that’s no longer a worry!
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