The term ’addiction’ can be used in several different ways. One definition describes physical addiction. This is a physiological state in which the body adapts to the presence of a drug so that the drug no longer has the same effect and the body requires more of the drug to maintain a ‘normal’ state. Nicotine, alcohol and caffeine are three common substances that result in physical addiction.
Addiction is also a condition that results when a person engages in a particular activity (e.g. gambling, sex, shopping) that can be pleasurable but can become compulsive and interfere with usual life responsibilities (relationships, work and even health).
Most activity-based addictive behaviour is a reaction to being emotionally stressed and the focus of the addiction isn't what matters; it's the requirement to take action, typically to obtain a short-term ‘lift’ brought about by certain kinds of stress. Treating this type of addiction requires understanding the psychological reasons behind it.
It should be noted that addiction is not simply a search for pleasure and that it is not related to a person’s morality or character.
For more information see Psychology Today – Overview of Addiction.