碧云天，黄花地，西风紧，北雁南飞。这四句诗句出自唐代诗人杜甫的《登高》一诗，形容了登高远眺所见的景象。碧云天指的是天空中晴朗的蓝天，黄花地则是指山间金黄的花海。西风紧则表明风势较紧，北雁南飞则指的是秋季南迁的候鸟。这四句诗句通过形象生动的描写，表现出大自然的壮丽和景色的美丽。

The four phrases "碧云天，黄花地，西风紧，北雁南飞" come from a poem by the Tang Dynasty poet Du Fu titled "Ascending Heights". They describe the scenery seen when one is at a high altitude. "碧云天" refers to the clear blue sky, "黄花地" describes the golden flowers in the mountains, "西风紧" indicates strong winds blowing from the west, and "北雁南飞" represents the migratory birds flying south in autumn. Through vivid descriptions, these four phrases depict the grandeur and beauty of nature.