What does "Yue Jian Underworld" mean? I plan to move tomorrow. I read everything else in Huangdi's book but I don't understand "Yue Jian Underworld".

Moon-building underworld is a concept in Feng Shui, which refers to the act of building roads or buildings during a month of darkness.

In Feng Shui, night is considered a time when the yin energy is heavier, so construction activities during this time may have some adverse effects on the surrounding aura. However, this does not mean that construction activities must not be carried out during the period of building the underworld. The specifics need to be comprehensively considered based on the actual situation.

The "monthly construction of the underworld" appearing in the Yellow Emperor's book may mean that it is more appropriate or unfavorable to carry out construction activities within a specific time period. However, it should be noted that the content in the Yellow Emperor's Book may have certain historical and cultural backgrounds, so it may not be applicable to modern society.

If you are interested in Feng Shui, you can consult a professional for more accurate information and advice.