Traditionally, these are the three days before Ascension Day on which the litany is sung (or recited) in procession as an act of intercession. They originated in Vienne, France, in the fifth century when Bishop Mamertus introduced days of fasting and prayer to ward off a threatened disaster. In England they were associated with the blessing of the fields at planting. The vicar "beat the bounds" of the parish, processing around the fields reciting psalms and the litany. In the United States they have been associated with rural life and with agriculture and fishing. The propers in the BCP (pp. 207-208, 258-259, 930) have widened their scope to include commerce and industry and the stewardship of creation. The BCP also permits their celebration at other times to accommodate different regional growing seasons. The BOS contains material for a Rogation procession, including petitions to be added to the Great Litany and the prayers of the people. The term is from the Latin rogatio, "asking."
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.