If you've never heard the term before, a "revenge body" is the body you get after you lose weight to get back at someone who hurt you. It's supposed to be a way of making them regret treating you poorly and show them that you've moved on.
I find the concept of a revenge body completely ridiculous. It propagates the idea that the only way to stop being dissatisfied with your body is by losing weight. Some people certainly are happier after losing weight, although I feel like a lot of that happiness is tied up in the belief that thin equals beautiful. But losing weight doesn't always lead to happiness. Just ask anyone who's suffered from an eating disorder. Losing weight made them miserable. It led them to spiral down into some of the darkest moments of their life.
Losing weight isn't the only way to start loving your body, nor is it even a guaranteed way to start loving your body. If you want to stop being unhappy with what you see in the mirror, try losing the hate instead of the weight. Changing your perspective is going to have a much bigger impact on your life than changing your body.
That's not to say that there's anything wrong with wanting to eat healthier foods and exercise more. Having balanced meals that give your body all of the nutrients that it needs helps you function at your best. Exercise can reduce stress, improve your mood, and help you sleep. These are both good things to incorporate into your lifestyle, but it's also important that you're incorporating them into your lifestyle for the right reasons (i.e. for yourself).
Labeling your post-weight loss body as a "revenge body" is basically you saying "Hey, remember when I was fat? I was just kidding when I looked like that. That wasn't the real me. That was a mistake. I promise I'm not supposed to look like that. I'm supposed to look like this. This is the real me."
No body is a mistake, no matter how much it weighs or what it looks like, and the real you is whoever you are in the moment.
Changing who you are to get back at someone doesn't make you stronger or better because you're still spending your time and energy on them. All you're doing by trying to get back at someone by losing weight is supporting the idea that your worth is dependent on your physical appearance.
If you really want "revenge", be happy with who you are. Stop judging yourself by the standards that someone else forced on you. Stop acting, feeling, and thinking within the parameters that someone else set for you. That's the ultimate revenge; being happy, even when someone is telling you that you can't or shouldn't be.