Zouri are flat and thonged Japanese sandals made of rice straw or other plant fibers, cloth, lacquered wood, leather, rubber, or synthetic materials. Zouri are quite similar to flip-flops.
The traditional forms of zouri are seen when worn with other traditional clothing; modern forms are fairly common, especially in summer. While geta are nowadays worn with the informal yukata, zouri are associated with the more formal kimono.
High-heeled version of zouri exists (link) and they are used in conjuction with furisode.