FIDL (formerly known as mojom) is an IDL and encoding format used to describe interfaces to be used on top of magenta message pipes. They are the standard way applications talk to each other in Fuchsia.
FIDL includes libraries and tools for generating bindings from .fidl for
supported languages. Currently, the supported languages include C, C++, Dart and
Go.
The language-fidl plugin provides syntax highlighting for
FIDL files in Atom.