Penso que este artigo explica bem o termo:

The 6-Traits Writing Model is made up of six key qualities that define strong writing:
Ideas - the main message;
Organization - the internal structure of the piece of writing;
Voice - the personal tone and flavor of the author’s message;
Word Choice - the vocabulary a writer chooses to convey meaning;
Sentence Fluency - the rhythm and flow of the language; and
Conventions - the mechanical correctness.
You should see these traits described and displayed in your child’s classroom and in other locations in our schools. We are excited to offer this motivating and effective approach to writing instruction to our students!

6 Traits Writing Model: Definitions and Icons
Introduction
The 6 Traits Writing Model for assessing and teaching writing is made up of six key qualities that define strong writing:
Ideas - the main message
Organization - the internal structure of the piece
Voice - the personal tone and flavor of the author's message
Word Choice - the vocabulary a writer chooses to convey meaning
Sentence Fluency - the rhythm and flow of the language
Conventions - the mechanical correctness
https://www.sd113a.org/academics/six-traits-writing

https://www.passeidireto.com/arquivo/2733097/qualidades-de-u...

Do que li do artigo em inglês, diria que é um modelo a seguir para uma escrita cuidada, para escrever bem: "qualidades da (expressão) escrita" ("traits of writing").