晴雨表 literally means 'clear-weather–rain–meter', combining 晴 (clear/sunny), 雨 (rain), and 表 (meter/instrument). Historically, it referred to a barometer that measures atmospheric pressure to forecast weather — hence the name, as it 'indicates' both sunny and rainy conditions. Today, it’s used almost exclusively in a figurative sense: as a metaphor for any sensitive indicator of broader trends or changes in a system — such as economic health, public sentiment, or social dynamics.

This word appears frequently in formal writing, news reports, and academic analysis — rarely in casual speech. It carries a slightly literary or analytical tone and often appears after words like '经济' (economy), '社会' (society), or '民心' (public opinion) to signal that the subject reflects deeper underlying shifts. Its power lies in implying responsiveness, sensitivity, and predictive value — not just passive measurement.