Aggression is defined as threats or harmful actions directed toward another individual. In animals, aggressive behaviors are a means of communication. Aggression describes the behavior, but does not give any information about underlying motives or causes.
Aggression can have multiple motivations.
Aggression can be subdivided into type based on intended victim, body postures during aggression, and other factors such as the animal may want, estrus status of animals involved, and location of the aggressive encounter. These encounters can involve fighting, escape, dominant and submissive gestures and posturing. Aggressive behavior can also be divided into offensive and defensive aggression. Note that there is no one single cause of aggression. Many factors and stimuli may combine to push the dog or cat to a point where aggression is displayed.