A polyglot is defined as one who is fluent in multiple
languages. This is similar to how a multilinguist is ... uh
...fluent in multiple languages. (OK, who invented two words for
the same concept?) Well, it turns out polyglot applies not only
to spoken languages, but to programming languages as well. Thus
in the software world, a polyglot application is one built on
multiple languages. The term also applies to developer tools
that can manipulate such apps.