1. words 2. visual representations — typography, icons and more: what the user ‘sees’ 3. physical objects and space — I think of this as ‘context’, whether — in our world of government services — the interface is sat on a desktop, in the user’s hand, used on a flaky mobile network, in an office or home, in a public space, on the move 4. time — things that change over time like sound and video
Why we call it interaction design
Andrew Travers
701

This is spot on.