A
collection of
unpublished material, often including
letters,
journals,
diaries,
receipts, etc.
An archive is composed of one or more collections, each of which was collected (or is being collected) for a specific purpose. The specific purpose specific purpose is outlined in the archives collections policy. The unit of measure of a collection is the linear foot.
An archive differs from a library in that a libraries major content is published material, and libraries generally catalog individual documents rather than entire collections.