You have probably eaten and heard about rice crackers. Senbei is a Japanese variant. It comes in a lot of variations. Common Senbei have a soy sauce flavor but nowadays the they can be had in many flavors. Sugar, Wasabi, seaweed, squid, curry, spicy, they are all there. There a lot of specialty shops and many regions have their unique Senbei. In the supermarkets there is usually a full path dedicated to Senbei as well.
In touristic places there are sometimes Senbei shops, where you can enjoy seeing the Senbei being baked above a fire. The flavored sauce is applied to the Senbei by a brush and is slowly baked in to the Senbei giving it its unique taste. The size is often similar to that of a dining plate.