Oops! You are right... LandXML.
It is an XML specification to allow the transfer of terrain and other data between different CAD applications. See http://landxml.org/
. So if you create a TIN in TurboCAD Civil you can export it in this XML format and then import into say AutoCAD Civil as a TIN. Most of the major Civil CAD applications support it. The emphasis here is on the transfer of terrain data as a TIN - Triangular Irregular Network.