TBX (TermBase eXchange) is a system for the exchange of terminological data. It is an ISO standard (number 30042) and an industry standard (formerly from LISA; now from ETSI). It includes a family of XML markup languages (called TMLs, for Terminological Markup Languages; also called TBX dialects).
If you are not already familiar with TBX, you might want to read a 2012 "JosTrans" article about terminology management that includes an introduction to TBX in section 4. If you are new to terminology management, please read the entire article.
For more information on TBX including the TBX standard itself, see an archive of OSCAR standards that mirrors resources formerly maintained by LISA (Localization Industry Standards Association), which closed its doors in March 2011.
You can find out about free and open source utilities for creating TBX files, converting to and from TBX files, and checking TBX files for compliance to the TBX standard, please see the TBX utility site.