Ambulatory
A sheltered place in which to walk, such as a gallery of a cloister or the outside aisle of a church. It is sometimes called the apse aisle. It may also be a passageway in back of the altar used for a procession.
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.