In biology, a type is that which fixes a name to a taxon. Depending on the nomenclature code which is applied to the organism in question, a type may be a specimen, culture, illustration, description or taxon.
For example, the Natural History Museum in London has a specimen numbered 18220.127.116.11 of the Spotted Harrier (Circus assimilis), which is the holotype for that species; the name Circus assimilis refers, by definition, to the species of that particular specimen.
Note that at least for type specimens there is no requirement for a "typical" individual to be used. When describing new species, this is often impossible to tell anyway, until more research has been done. Genera and families, particularly those established by early taxonomists, tend to be named after species that are more "typical" for them, but here too this is not always the case and due to changes in systematics cannot be. Hence, the term name-bearing type or onomatophore is sometimes used, to denote the fact that biological types do not define "typical" individuals or (in zoology) taxa, but rather fix a scientific name to a specific operational taxonomic unit. Type specimens are theoretically even allowed to be aberrant or deformed individuals or color variations, though this is rarely the case as it makes it hard to determine to which population the individual belonged.