That is the dictionary's definition. My definition is a living thing. It's relentless fatigue, that can make getting out of bed virtually impossible. It's "fibro fog", which is like trying to think while buried in sand. It's pain, that when it's bad, wearing a shirt is excruciating. It's about learning to live with limitations, so that the pain and fatigue are manageable. Instead of being able to accomplish many different tasks throughout the day, you pick one or two that are most important. Then rest.
It has taken many years to learn to live with fibromyalgia. I went through the many stages of grief when diagnosed. Anger, fear, depression, defeat and acceptance. You grieve for what you once could do. You're mad that you can no longer do those things. You become depressed. You become defeated. Then you finally accept your limitations. It is at that stage that you begin to heal. You learn to live fully within those limitations. You learn strategies for lessening the pain and the fatigue. They are constant companions so you must learn to live with them. I still have bad days, but I have learned to cope with them.