singularity; peculiarity; idiosyncrasy; specificity
Refers to a distinctive or unusual quality that sets something apart. Used in both everyday and technical contexts.
The culture of this region has a distinctive character.
They are researching the specificity of that disease.
特殊性 also means 'particularity' or 'specificity', but 特異性 often carries a stronger nuance of being unusual or idiosyncratic.
Compound of 特異 (とくい, 'unique, peculiar') + 性 (せい, '-ness, -ity'). The exact historical derivation is uncertain; the spelling is conventionally associated with the meaning.