In my last counseling session with my son the counselor as him to define addiction - he had memorized it as "when we habitually or compulsively - with or without awareness or intention - use any activity, substance or person[s] to move us away from our true selves." no where in the definition does it say how often only that its habitual and compulsive.
My personal definition is anything we do repeatedly that affects our lives no matter what the consequences are. This can be anything, alcohol, drugs, porn, gambling, sex, computers, shopping, eating - if we do these things without regard to how they affect our lives or the lives of our loved ones then we have a problem. It doesnt matter the frequency only the effect on our lives.