Converter
A converter is a specification, in the form of a handlebars expression, for constructing a text that a particular text conversion tool uses to create its output.
The specifications of the particular tool tell you which converters are predefined for that tool, and what the converter profile is that a customized converter may use.
Editor's note
We could perhaps add references to appropriate sections of relevant tools, so that readers can see examples of this.
The generic workings of converters is documented in the TEv2 Text Conversion pattern.