Generally a reflecting pool is just a small, shallow, calm pool of water in which reflections can be seen. Today I was walking up 4th Street just past Folsom in San Francisco and off to my left I noticed a reflecting pool on the side of a building. The whole side of this building is covered with little hanging mirrors that blow in the wind and make the same patterns you'd see on a pond with wind blowing across it, but on the side of a building.