The response of assent by the congregation at the conclusion of the eucharistic prayer. As the eucharistic celebration is shared by the congregation and the presider, the Great Amen emphasizes the assent of the people to the words spoken on their behalf by the presider. The Great Amen is the "people's prayer" that concludes the eucharistic prayer. The Great Amen is printed in all capital letters in the BCP to emphasize the importance of this moment in the liturgy. Historically, the "moment of consecration" at the eucharist was considered to be the institution narrative in the western church. Some eastern churches understood the epiclesis (invocation of the Holy Spirit) to be the moment of consecration. However, the eucharistic prayer (including institution narrative and epiclesis) is now understood to be a single text, with the consecration completed as the eucharistic prayer concludes with the people's Great Amen.
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.