What does it mean to be frozen underground?

It means: describe the weather as particularly cold. Generally used as an idiom, it can be expressed as: freezing in the cold.

It's freezing:

Describe the extremely cold weather.

[Allusions] Chapter 65 of Shi Ming Naian's Biography of the Water Margin: "Today's eyes are frozen, and it is difficult for the army to stay for a long time. I can go back to the mountain."

[Synonym] A thousand miles of ice is frozen and dripping into ice.

[antonym] The sun is scorching, and the sun is like fire.

[useful] useful

[emotional color] commendatory term

[Grammatical Usage] As a predicate; Describe the weather is very cold.

[Idiom structure] Combination form

[Date of birth] Ancient times

Extended data:

Synonym: dripping into ice

Water drops will turn into ice. Describe the cold weather.

[Allusions] Song Qian Yi's new book "Songs of the South": "Winter is cold, dripping into ice."

It's very cold, and water drops will turn into ice.

[Synonym] icehouse, ice and snow

[antonym] The sun is like fire, the scorching sun is scorching, and the weather is sunny.

[useful] useful

[emotional color] commendatory term

[Grammatical Usage] Concurrent language; As predicate and attribute; Describe the weather is very cold.

[Idiom structure] Serial form

[Date of birth] Ancient times