What is anger? Most people have a hard time coming up with a definition of it, some may say its yelling others may say its a feeling, others may say they can't describe it but know it when they see it.
The definition I use for anger is that its a protective response to a perceived hurt or threat. Think about it - have you ever gotten mad when something important to you (be it pride, a possession, a family member, etc...) wasn't being threatened or hurt in some way? Anger is a way to mobilize yourself for protection.