The term originates from adoptive and academic circles to describe the very lived experience of children raised in homes that are phenotypically and culturally different from their birth.
Most recently, and thanks mostly to Rachel Dolezal, the term transracial has been changed to mean ‘people who claim to have a racial identity that differs from their birth race’. Apparently genetics no longer matter. In the case of Miss Dolezal, she was born Caucasian from Caucasian parents, but grew up with black siblings. Specifically, transracial would apply to them.