Paper which has had the acid removed from the pulp so that it has a neutral 7.0 pH (or above).
The acid normally found in paper can discolor it over time and turn it brittle. Photos printed on papers with acid will be altered and can fade and even eventually disintegrate. Paints and items that come into contact with the acid paper such as photos in photo albums or items in a collage will have a shortened life.
The use of acid free paper can prolong the life of a document or project printed on, painted on, or attached to the paper.
See also: archival paper