What do "Small Cold" and "Big Cold" in the twenty-four solar terms mean?

Xiaohan is the 23rd solar term among the 24 solar terms of the lunar calendar and the fifth solar term in winter, marking the official start of the winter season. When the sun reaches ecliptic longitude 285° (Little Cold), it marks the arrival of the coldest day of the year for China.

Dahan is the last solar term of Xiaohan. It is the last solar term among the twenty-four solar terms throughout the year. Every year around January 20 of the Gregorian calendar, when the sun reaches 300° of ecliptic longitude, it is the Great Cold.

Classical records:

Xiaohan, December Festival. The cold at the beginning of the month is still small, so it is said. Half a month is big.

The Great Cold is the middle one, and it is superior to the Lesser Cold, so it is called Great... The cold is the opposite extreme, so it is called Great Cold.