五 (wǔ): The number five. In this context, it doesn't mean literally five, but rather “all” or “various kinds.”
谷 (gǔ): Grain, cereal, or crop. “五谷” (wǔgǔ), the “five grains,” is a classical term for all staple food crops in China (traditionally including rice, wheat, millet, etc.).
丰 (fēng): Abundant, plentiful, rich, bountiful.
登 (dēng): This character can mean “to ascend” or “to climb,” but here it carries an older meaning of “to ripen” or “to be harvested and brought to the granary.”
The characters combine to create a powerful image: “The many kinds of grain are abundant and ripe for harvest.” This directly translates to the concept of a massive, successful harvest, which in turn symbolizes a prosperous and stable society.
`五谷丰登` is considered a formal and auspicious (吉利, jílì) phrase. Its usage is generally reserved for situations where you want to express a grand, positive vision.
Festivals and Blessings: This is the most common use today. During Chinese New Year, you will see `五谷丰登` on decorations, in official speeches, and used in greetings to wish for a prosperous year ahead for the family or the country.
Official and Media Language: Government reports and news articles often use `五谷丰登` to describe a good year for the agricultural sector or to set a positive tone when discussing the national economy.
Describing Art and History: It can be used to describe traditional paintings (年画, niánhuà) that depict scenes of a joyful harvest or to talk about “golden ages” in Chinese history.
It is generally not used in casual, everyday conversation for small-scale successes. It's a “big picture” term.