From the Greek mystagogos, the term refers to a process of initiation into "mysteries." It may take place after baptism at the Easter Vigil, lasting throughout the Great Fifty Days of the Easter season. It involves the integration of adult neophytes into the life of the church. It is less strictly defined than the catechumenate. Members of the Christian community continue to help and instruct the new Christians. The BOS notes that "This period is devoted to such activities, formal and informal, as will assist the newly baptized to experience the fullness of the corporate life of the Church and to gain a deeper understanding of the meaning of the Sacraments." In the broadest sense, Christians live in mystagogia for the rest of their lives as they continue to enter into the mystery of Christ's death and resurrection.
Glossary definitions provided courtesy of Church Publishing Incorporated, New York, NY,(All Rights reserved) from "An Episcopal Dictionary of the Church, A User Friendly Reference for Episcopalians," Don S. Armentrout and Robert Boak Slocum, editors.