I'd say distributed cross-platform cross-device application.
- distributed - when the application uses a network
- cross-platform - when the application is aware of multiple platforms, for example it works on unix and windows as well
- cross-device - when the application is aware of different hardware types, for example it displays a metro gui by touchscreen and normal webpage by mouse + keyboard
- cross-browser - when the application runs in a browsers, and it is aware of different browser types, for example it uses CORS by firefox and chrome, but by msie it tries an alternative approach to connect to the server, or displays a fallback
- heterogeneous system - when you application uses different hardware and software types to achieve its goal, for example it has a php frontend tier and a java backend tier, etc...
- polyglot - when the application uses multiple programming languages to achieve its goals, for example by polyglot persistence you use nosql and sql databases as well