The traditional East Asian calendars divide a year into 24 solar terms (節氣). Lìchūn (pīnyīn) or Risshun (rōmaji) (Chinese and Japanese: 立春; Korean: 입춘; Vietnamese: Lập xuân; literally: "start of spring") is the 1^st solar term. It begins when the Sun reaches the celestial longitude of 315° and ends when it reaches the longitude of 330°. It more often refers in particular to the day when the Sun is exactly at the celestial longitude of 315°. In the Gregorian calendar, it usually begins around February 4 and ends around February 18 (February 19 East Asia time). It's also the beginning of a Sexagenary cycle.

Source: JPL Horizons On-Line Ephemeris System

Each solar term can be divided into 3 pentads (候). They are: first pentad (初候), second pentad (次候) and last pentad (末候). Pentads in Lichun include:

It is not called the 'winter ice meets the spring wind and melts in the spring wind' thaw, but the 'east wind' thaw, because Lü Shi Chun Qiu said that the east is associated with wood, and wood generates fire, so the air is warm and causes ice to thaw. (凍結于冬遇春風而解散不曰春而曰東者呂氏春秋曰東方屬木木火母也然氣溫故解凍)