Definition of "HIIT"

Perhaps I would struggle to do a HIIT session.

2021, Dr Philippa Kaye, Doctors Get Cancer Too, Vie Books, page 151

HIIT’s specific origins are uncertain; some say it dates back to at least the early 1900s and Finnish Olympic runners who would use alternating short bursts of intensity with brief bouts of recovery to bolster their overall speed.

2023 March 15, Amanda Loudin, “A 19-Minute HIIT Workout for Beginners”, in The New York Times‎