camp meeting

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An evangelistic gathering held in a tent or outdoors and often lasting several days.

from The Century Dictionary.

• noun A religious gathering for prayer, instruction, exhortation, etc., held in an encampment formed in a wood, grove, or field, generally continued for a week or more.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun religious (usually evangelistic) meeting held in a large tent or outdoors and lasting several days