A glacier is a large, slow-moving mass of ice formed from snowfall and melting ice over thousands or millions of years. They are found in cold regions such as Alaska, Greenland, Antarctica, and the Arctic, where temperatures remain below freezing for most of the year. Glaciers move very slowly due to their immense size and weight, carving out valleys and shaping landscapes along their path. They are also important indicators of climate change as they reflect changes in temperature and precipitation patterns over time.