An addict is a person that is in deep emotional pain, disconnected from other people and from nature. Addictions come with depression and with a broken environment. If you want to solve your addictions, solve your emotional pain first, live through the hard, unpleasant, painful emotions and feelings. If you want to solve your depression, then change your environment. It's hard, but the only way to get over addiction and environmental depression.
I think an addict is an unhealthy obsession and reliability on something. If someone constantly feels urges to do/use something, and does/uses it constantly, they're an addict.