"Keyi" is a fundamental term in Taoism. Taoism is defined as a religion not only by its systematic doctrines and beliefs but also by its specific religious rituals, which encapsulate the content of its spiritual methods.

The liturgical rites of the Zhengyi School are numerous and varied, ranging in specification and scale. In ancient times, the highest specification and largest scale was known as the "National Offering" (國醮). Today, the highest specification within Taoism is the "Grand Offering of the All-Encompassing Heaven" (羅天大醮).

Specifically regarding individuals, these rites can be broadly categorized into two types: Yang Matters (for the living) and Yin Matters (for the deceased). Based on the needs of the Benefactor (福主), the corresponding rite can be performed to achieve the goals of praying for blessings and dispelling disasters.

Keyi follows a rigorous operational procedure. Its internal mechanisms involve numerous secret oral instructions (法訣) and the esoteric lineage transmissions of the Zhengyi School. Therefore, it stands as the core hallmark of the Zhengyi tradition.