NASA found evidence of ice on Mars. What does that mean?

NASA's Mars-orbiting satellite, the Mars Reconnaissance Orbiter, carries a powerful camera called the High Resolution Imaging Experiment (HiRISE) that captures rich imagery of the Red Planet's surface (it's the "most powerful camera ever sent to another planet," the HiRISE team explains). Recently, planetary scientists used HiRISE to snap an image of a glacier-like "icy flow," taken from 184 miles above Mars' surface. Frozen ice doesn't only exist in the frigid Martian poles.