A collection of unpublished material, often including letters, journals, diaries, receipts, etc.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.