by byronczimmer
Definition of liminal
1 :of, relating to, or situated at a sensory threshold :barely perceptible or capable of eliciting a response
liminal visual stimuli
2 :of, relating to, or being an intermediate state, phase, or condition :in-between, transitional
in the liminal state between life and death —Deborah Jowitt
Never defines the term, and as far as I can tell, doesn't prove the point.
I hope that the author's academic career isn't dependent upon this analysis.