The term "destructive anger" comes from Seeking Safety, an effective treatment for PTSD and substance use.
Constructive anger is anger that can be healing. Constructive anger is often lower in intensity than its counterpart, destructive anger. It is also something that can be explored or examined to help you better understand your situation, other people, and yourself. Further, for anger to be constructive, a person must also be aware of that anger. Finally, constructive anger is something that is managed appropriately, with respect given to your own needs and the needs of others.
As an example of constructive anger, let's say that a friend cancels an important lunch date with you at the last minute. By approaching your anger and listening to what it is telling you, you might be motivated to talk to your friend about how you were upset by the last-minute cancellation and come up with ways to make sure that it doesn't happen again. The anger in this situation is being used to take control over the situation and maintain your self-respect.