What does Sanjiu mean?

A certain period in the traditional lunar year in China is also called "Sanjiu". There's a saying in China, "Practice dog days in summer, practice Sanjiu in winter". Corresponding to three nine is three volts. "March 9th" refers to the third "nine days" after the winter solstice, that is, the 19th to 27th days after the winter solstice. "The third nine days after the winter solstice" refers to "March 99", which is also the day when March 99 and April 99 intersect, not "March 99", that is, "March 99" is nine days instead of one day. People say, "it's cold for nine, and it's cold for nine in March." "March 9th" generally appears in the winter from solstice to shock.