Interaction Design is a field and approach to designing interactive experiences. These could be in any medium, not only digital media. Interactive experiences, necessarily, require time as an organizing principle (though not exclusively) and Interactive Design is concerned with a user, customer, audience, or participant's experience flow through time. Interactivity should not be confused with animation in which objects may move on a screen; interactivity is concerned with being part of the action of a system or performance and not merely watching the action passively.
I recently conducted a study into the helpfulness (or lack thereof) of zebra striping—the shading of alternate rows in a table or form. The study measured performance as users completed a series of tasks and found no statistically significant improvement in accuracy—and very little statistically significant improvement in speed when zebra stripes were implemented.
Digital interfaces are full of motion. In fact, the UX application of UI motion design has become so important, it’s taking on new terminology of its own—UX choreography. It includes interaction design, motion-based transitions, micro-interactions, and motion that supports the overall brand personality.
Email, the web’s much maligned little cousin, is in the midst of a revolution—one that will change not only how designers and developers build HTML email campaigns, but also the way in which subscribers interact with those campaigns.