You could be restricting calories from where you began and not where you are.
You can refrain from eating a donut, i.e calorie restriction. Or you can eat it and not restrict calories. You don’t have to be losing weight to restrict calories, it can also be for maintenance.
So anyone who isn’t actively gaining weight is on a Calorie Restriction Diet.
Not necessarily. It’s when you restrict calories from ad libitum often in the already healthy weight range.
In the Minnesota Starvation Experiment by Ancel Keys the participants had their calories cut in half, they had numerous side effects and eventually stabilized in weight. They were calorie restricted. Eventually they got to eat whatever they wanted and regained the weight back and the symptoms disappeared.