Terzie is the second daughter and middle child of Lord Barak and Lady Merel of Trellheim. Her estimated birth year is 5362-5364. She has an older sister, Gundred, who is described "only slightly older than Errand" (Castle of Wizardry) with long reddish-blond braids. Terzie also has these long reddish-blond braids. She is a year or so younger than Gundred.

By the time of the birth of Geran, she is described as hovering on the brink of womanhood: romping with the younger children one moment and looking the next with devastating eyes at the group of adolescent Rivan boys who always seemed to be around.

She seems to be less self-conscious than her older sister, Gundred, especially in receiving the affections of her father, Barak.