炉 (lú) is a bound morpheme meaning 'stove' or 'furnace.' You will most often encounter it as the root in compound words like 炉子 (stove), 电炉 (electric stove/furnace), and 火炉 (heater/brazier). It cannot stand alone as a free word; when you see it in writing, it is usually attached to another character. Additionally, 炉 is commonly used as a classifier (measure word) for fires in expressions like 一炉火 (a fire), though this usage is separate from its bound-form status.