I wasn't sure what a flare was till I had one. My usual slight aches after each reduction had always resolved within a week or so, followed by a couple of weeks of being ache and pain free till the next reduction. A small early evening dose (split dose) meant I had zero pain at any time, including mornings.

Then one time the aches didn't resolve before the next reduction was due and I knew something was different, but the aches were minor, so I reduced another .5mg. Then the aches became minor pain, not just stiffness and aches, and over a few weeks the pain went from 1-2/10 to 5-6/10, and I rang the doctor to say I was having a flare. It couldn't be left any longer by then - doorknobs were hard to open, I couldn't lift things any more, and it was getting worse. Blood tests confirmed that inflammation had risen again. That's a flare.