Possible interpretations:
* Variations of other names: It could be a variation of names like "Tian" (meaning "heaven" or "sky" in Chinese) or "Tiana" (a name of Italian origin).
* Made-up name: Some parents choose to create unique names for their children.
Without more context, it's impossible to determine the exact meaning of "Tiahn." If you're interested in learning more, you could try contacting the parents or asking them about the origin of the name.