干干净净 is the reduplicated form of 干净 (qīngjié/gānjìng, meaning 'clean'). The AABB pattern intensifies the meaning — it describes something as thoroughly clean or spotless. It can also be used as a complement after verbs to mean 'completely, leaving nothing behind' (e.g., 吃得干干净净 'eat everything up'). In spoken Chinese, the tone on the second 干 is often slightly reduced, but standard pinyin writes it as gān gān jìng jìng.