The term “gaslighting” comes from the movie, and so its definition is rather specific: when a person lies for their own gain to another person so repeatedly and with so much confidence that the victim begins to doubt her own sanity. And, as the film puts it, a bit of Stockholm Syndrome develops as well: the victim, now uncertain that she can perceive reality correctly, becomes dependent on the gaslighter, more attached to him than ever.
I think there’s also a slighlty nuanced version that people use a lot: when the “bad actor” isnt lying, and thinks their case is correct. In this case, the bad actor is trying to make the “victem” think it’s all their fault, usuaully due to the old pop-Frueden move of identifitig hidden, unknown, and otherwise uncioicious motivations, or, just being ignorent and “dumb.”
To the victim, it all looks the same, but the difference is that the bad actor isn’t lying: so they believe they’re fighting for the truth.