herbarium (plural: herbaria) is a collection of preserved plant specimens and associated data used for scientific study. These specimens may be whole plants or plant parts: these will usually be in dried form mounted on a sheet but, depending upon the material, may also be kept in alcohol or other preservative.
The term can also refer to the building or room where the specimens are housed, or to the scientific institute that not only stores but uses them for research and study. The specimens in a herbarium are often used as reference material in describing plant taxa; some specimens may be types.
The same term is often used in mycology to describe an equivalent collection of preserved fungi, otherwise known as a fungarium. A xylarium is a herbarium specialising in specimens of wood. The term hortorium (as in the Liberty Hyde Bailey Hortorium) has occasionally be applied to a herbarium specialising in preserving material of horticultural origin.