Two related senses: (1) a primitive kiln dug into a hillside or pit for firing bricks, lime, or charcoal; (2) on the Loess Plateau (
黄土高原) of Shaanxi and Shanxi,
土窑 means
窑洞 (yáodòng) — cave dwellings carved into the loess cliffs that have housed millions for centuries. Mao Zedong famously lived in one in Yan'an during the 1930s-40s.