Addiction is when the motivation for a stimuli is divorced from reward from the stimuli and the animal keeps exposing itself to the stimuli regardless. But socially in humans this is acceptable until the addiction begins to have detrimental effects on the person being able to care for themselves. In almost all cases the simuli capable of doing this are drugs that bypass actual perception and internally/chemically tweak the balance for motivation.

There's not even a thing called "Gambling Addiction". Only, "Gambling disorder" and it's the only behavioral "addiction" recognized by the DSM-5.