Type Description Language (TDL) is the name of a data type specification language defined in the book Implementing Typed Feature Structure Grammars.
It is a modeling language specifically used to describe an ontology of HPSG types, these are typically used to model natural language phenomena. The LinGO suite, amongst other DELPH-IN (Deep Linguistic Processing with HPSG) open-source project. software and implementations, utilize TDL.
References
Type Description Language Wikipedia(Text) CC BY-SA