V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

NRZI
       Non-Return-to-Zero, Invert to ones [encoding]


The Free On-line Dictionary of Computing (30 December 2018):

Non Return to Zero Inverted
NRZI

    (NRZI) A recording method used for 9-track magnetic
   tapes (200 and 800 BPI) where a zero is represented by a
   change in the signal and a one by no change.

   NRZI is also used extensively in SDLC communications.
   VTAM has a parameter NRZI=YES|NO.

   Compare Phase Encoded, GCR.

   (1999-01-11)