Archives use terminology that may be unfamiliar to new researchers. If you are doing any kind of archival research, there are a few terms you should familiarize yourself with:
A group of documents of any provenance that is intentionally assembled based on subject, form, geographic scope, or some other common characteristic.
The entire body of records of an organization, family, or individual that have been created and accumulated as the result of an organic process. Fonds are typically arranged into:
Series: Documents arranged systematically or maintained as a unit because they relate to a particular function or subject, result from the same activity, have a particular form, or because of some other relationship arising out of their creation or, arising out of their receipt and use. Many series contain groups of related papers that can be grouped under sub-series.
File: An organized unit of documents, usually within a series, brought together because they relate to the same subject, activity, or transaction.
Item: An archival unit that can be distinguished from a group and that is complete in itself. Items are usually found within files
Check the How is archival material organized? page for a diagram that illustrates the hierarchical structure of a fonds.