The characters literally combine to mean “to pour pure ghee onto the crown of the head.” This vivid image originates from a Buddhist ritual symbolizing the bestowing of supreme wisdom and blessings. Metaphorically, it describes a moment where profound wisdom is “poured” into your mind, leading to instant enlightenment.
This idiom is common in both written and spoken Chinese, though it carries a literary and formal weight. It's used to express sincere and profound gratitude for eye-opening advice or instruction.