According to the dictionary, addiction is : a habit that has become impossible to break, especially one involving physical and psychological dependence on the intake of harmful substance such as drugs or alcohol (Harrap's Chambers).
We all know about alcohol and drug's addictions and so I will not bother talking about it. I will just say that those addictions are the result of former stealth addictions that our society offers in a wide variety.
We are addicted to our television on which we spend a fair amount of time watching, of our smart phone that we take everywhere and on which we don't take our eyes off, ignoring our direct surrounding. For those of us who own a car, they will use it more than necessary. Addiction extend also to material possession to which we have hard time to part with (often because we need them, but also for sentimental or social status reasons). And as Tyler Durden was saying in 'Fight Club' : things that we own end up owning us. He was himself using that adage from ancient wisdoms.
But material possessions isn't the sole responsible for our addiction. Our lifestyle can be a source of addiction, for example our endless desire of intense sensations, or, on another hand, this quest for stability that generates all those habits, and which I believe to be stagnation.
What creates this addiction ? many things, but one that is particularly important, I believe : attachment or affection, even though it does not systematically lead to addiction.
I will say then, that addiction is an attachment to a thing or a situation that provide a great pleasure combined to a refusal of seeing it end.