Type specimens are references for scientists to refer back to for identification purposes, meaning these specific specimens have clearly identifiable features that define the species. Often these types have been figured in peer-reviewed publications. There are many different forms of type specimens, all of these types are stored in specific museum collections.
Holotype: this is the name bearing specimen, often this is the specimen that is found and first described to have this name.
Paratype: additional specimens that are added to the description at the original time of description.
Holotypes and paratypes are the primary types and all species have them! The conditions of these types can vary. A holotype of a brachiopod will likely be a pristine specimen but a holotype of a dinosaur may only be a single tooth.
Here are a few other types that are commonly found in museums:
Neotype: this specimen replaces the holotype if the holotype has been lost, destroyed, or the original author did not name one.
Syntype: this can be two or more specimens that are explictly named in a species description where no holotype was assigned.