Work addiction is where the individual spends most of their time and most of their focus on work. Work is the place they get good feelings, work is the place they get rewarded, work is the place they get excited and optimistic about life.

Work is the place they feel sort of buffered against the loneliness or estrangement that they might feel at home or in other domains.

Work addiction is just one manifestation of a variety of behavioral addictions where work, which is a normal, healthy process we all engage in, is the place where the rewards come, the good feelings come from, and it's actually engaged in to a degree where other domains of their life go unattended to and neglected.