Learn
The 24 solar terms
The Chinese year has 24 solar terms; they mark the seasons, not the moon.
Solar terms divide the sun's year into 24 parts. They are why the almanac's "season" line matters even in a purely lunar calendar.
Why they exist
A lunar month is 29.5 days; twelve of them fall eleven days short of a solar year. Solar terms keep the calendar anchored to the sun, so planting, festivals and the almanac's season notes stay in the right part of the year.
What GoodOmen shows
The next term and how many days away it is, with the date. Terms are also where the month pillar changes, which is why a birth chart's month can change in the middle of a Gregorian month.