It's possible that "triadic sentence" is a term used in a specific context or academic discipline, but without further information, it's difficult to define its meaning.
Here are some possible interpretations:
* A sentence with three main parts: This could refer to a sentence with a subject, verb, and direct object. However, this is a common sentence structure, not a specific type.
* A sentence with three clauses: This could be a complex sentence with three independent clauses or a compound sentence with three dependent clauses.
* A sentence that expresses a relationship between three entities: This could be a sentence that describes a connection or interaction between three people, objects, or concepts.
If you can provide more context or information about where you encountered the term "triadic sentence," I might be able to give you a more specific answer.