What does sui generis mean?
Sui generis
For example, in road traffic law, a statute may require consideration of large vehicles separately from other vehicles.  The word large is ambiguous per se, but may be considered heavy.  Thus the relevant legislation (in Australian law) contains a section called Terms used or Definitions that itemises all words considered ambiguous, and confers specific interpretations consistent with natural language.  So, this list tells us that heavy vehicle means a vehicle with a GVM over 4.5 tons; and GVM means gross vehicle mass—the maximum loaded mass of the vehicle. Further explanations cover various contingencies.  Thus large is equivalent to heavy and is (for this unique case) clearly defined, sui generis.