“Wu” here refers to the fifth day by the “Tian Gan” time system.
According to the classics, on these days Heaven and Earth will go through certain shifts or changes. Therefore no ritual of any kind is allowed on “Wu” days, and breaking of this rule will bring hefty punishments.
According to the daoist calendar every 10 days is a “Wu Ri”. So every ten days the temples will not have any ceremony and the most daoist have a day of rest. On this day it is still possible to practice and study.
There are exeptions for this “rule” and in fact there are many rituals done on a Wu Ri.
书符 – Drawing Talisman
刻印 – Carve Seals
祭将 – Offering to Officers
祭雷 – Offering to Thunder
存神 – Retain Spirit
忏悔谢过 – Confessions & Apologize for wrong doing
刻令 – Carve Ling Tokken