holotype
n.the single physical example of a species that scientists use to define what that species looks like. It is the official 'standard' for that name.
n.the single physical specimen designated as the name-bearing type of a species. It serves as the permanent reference point for the taxonomic description of that organism.
“The museum houses the holotype of the newly discovered beetle.”
“When the researchers published their paper, they designated a specific fossil as the holotype to ensure future scientists could identify the species correctly.”
“In the event of a taxonomic dispute, the holotype provides the definitive morphological standard against which all other specimens must be compared to determine their classification.”
From holo- + -type.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.