Other forms: herbaria; herbariums
A herbarium is a collection of preserved plants. Think of it as a library of herbs.
A herbarium can be something as simple as that book of pressed flowers you made at summer camp, or as complex as a building that holds case after case of flowers soaked in formaldehyde, dried moss stored in archival quality envelopes, and cones from conifers organized in boxes. Find these larger collections at universities, botanical gardens, and natural history museums.