the place at which independent and often unrelated systems meet and act on or communicate with each other
the means by which interaction or communication is achieved at an interface
mutual or reciprocal action or influence
two entities that determine each other's behavior over time
[hornbæk and oulasvirta 2017]
entities: humans and computers
not just interplay
agency
causal relationship affected by design
Chapter 1: "What is Interaction Design?"
Interaction Design: Beyond Human-Computer Interaction