"So I'm not a Southern writer in the commonly held sense of the term, like Faulkner or Eudora Welty, who took the South for their entire literary environment and subject matter"

In this quote, Donna Tartt is resolving the category of authors based upon local affiliation, especially with regard to the Southern United States. She is drawing a difference between herself and other Southern authors who are deeply linked with the South in terms of styles, setting, and cultural focus.

Tartt points out William Faulkner and Eudora Welty as ultimate Southern writers. Both authors are renowned for their deep engagement with Southern settings, customs, and the distinct cultural atmospheres that specify the area. Faulkner's work, for instance, frequently explores the complexities of Southern identity, history, and social dynamics, set against the background of Mississippi. Similarly, Eudora Welty is known for stories that catch the intricate information of Southern life, frequently instilled with an understanding of its people and landscape.

By specifying she is not a "Southern author in the frequently held sense of the term", Tartt implies that, while she is from the South (Mississippi), her literary focus does not solely revolve around Southern styles, settings, or the expedition of Southern identity that defines the works of Faulkner or Welty. This suggests that Tartt's work may be more eclectic or universal in scope, examining human experiences that transcend local boundaries. Her books, such as "The Secret History" and "The Goldfinch", support this assertion, including diverse locations and themes that are not restricted to the Southern milieu.

Tartt might also be meaning the capacity for an author to simultaneously belong to a geographical area and transcend its standard literary confines. By declining a rigorous, regionalist label, she stresses the fluid nature of her narrative interests and the expansive possibilities open up to authors, despite their origins. Eventually, she underscores a broader, maybe more inclusive, understanding of identity and influence in literature.