  Fidelity describes how closely a replication resembles the original. It can
be helpful to analyze how faithful interactions in virtual reality (VR) are to
a reference interaction. In prior research, fidelity has been restricted to the
simulation of reality - also called realism. Our definition includes other
reference interactions, such as superpowers or fiction. Interaction fidelity is
a multilayered concept. Unfortunately, different aspects of fidelity have
either not been distinguished in scientific discourse or referred to with
inconsistent terminology. Therefore, we present the Interaction Fidelity Model
(IntFi Model). Based on the human-computer interaction loop, it systematically
covers all stages of VR interactions. The conceptual model establishes a clear
structure and precise definitions of eight distinct components. It was reviewed
through interviews with fourteen VR experts. We provide guidelines, diverse
examples, and educational material to universally apply the IntFi Model to any
VR experience. We identify common patterns and propose foundational research
opportunities.
