The first frost and cold dew are one of the 24 solar terms. The first frost is the eighteenth of the twenty-four solar terms and the last solar term in autumn. Cold dew is the seventeenth solar term among the twenty-four solar terms and the fifth solar term in autumn.

The first frost does not mean "frost", but refers to the sudden drop in temperature and the large temperature difference between day and night. On the national average, "first frost" is the season with the largest temperature difference between day and night in a year.

Cold dew is a festival in late autumn and the beginning of the full moon in the dry calendar. Cold dew is a solar term reflecting the characteristics of climate change. When entering the cold dew, there is cold air going south, the temperature difference between day and night is large, and autumn dryness is obvious.