Another one that confuses people is "MS is always active."

True: It never goes dormant. It can be stable, very slowly progressing, moderately progressing, or quickly progressing. It may not show up in relapse for years, even after your MS dx.

Then it can cause symptoms from heck, then it can go slowly again. You recover, and years later a problem again.

No rhythm or reason behind it. It does what it very well pleases. We can get pseudo-relapses too. They are not considered true relapses.

Example would be being in heat or hot sun and getting your symptoms to feel worse, like a true relapse is coming on. But cool off and don't overdo it, and it stops those problems in a few hours. Sort of like a fake relapse.

Relapse, exacerbation, and flare, are used as the same word and are the same. Those three have the same meaning.

During a relapse, a new symptom, or new lesion may appear somewhere (brain or spine). Also some old lesion/s may get inflamed (or attacked) again.

If the lesion/s get attacked too often and don't remyelinate even a little, they turn into black holes visible on MRI of the brain. A dead part (black hole).

It does get confusing. For years I mixed them up.