The traditional East Asian calendars divide a year into 24 solar terms. Xiàzhì, Geshi, Haji, or Hạ chí is the 10th solar term, and marks the summer solstice. It begins when the Sun reaches the celestial longitude of 90° and ends when it reaches the longitude of 105°. It more often refers in particular to the day when the Sun is exactly at the celestial longitude of 90°.
The solstices (as well as the equinoxes) mark the middle of the seasons in traditional East Asian calendars. Here, the Chinese character 至 means "extreme", which implies "solstices", so the term for the summer solstice directly signifies the summit of summer.