If your spin class is somewhat long like say 45 minutes with continuous work intervals of like a couple minutes or more and then a rest period, I’d say this is more of an interval type of training. It’s still great for heart health and such but is likely not a true HIIT where you do multiple bouts of high intensity followed by short rest periods. I do a HIIT workout on my bike trainer where I do a short warm up, then I do 12 – 20 seconds bursts followed by only 10 seconds rest and then I follow that with 10 intervals of 30 seconds on and 30 seconds off and a short cool down. And BAM, that’s 20 minutes and my HIIT is over. Hope this helps!