It’s important to distinguish between regular lying and gaslighting. A lie is just a falsehood and it can be told for many reasons.
Gaslighting are lies told with the specific intent to make the other person question their sanity/reality.
It is a form of manipulation to make the other person doubt themselves so much that they no longer trust their perception of events. If you no longer trust yourself, then you begin to think you are the problem and the other person is then off the hook.
A good example of gaslighting is when your husband comes home late from work for the 10th time in a row. You ask him why he keeps coming home late. “What?” He says, in shock. “I haven’t been coming home late! Are you sure you aren’t just losing track of time?” And you doubt yourself. The next day it happens again, but you checked the time. “You’re late!” And he said “what? No I’m not. I always come home at this time.” And you try to argue that it’s only been the last ten or even times he shows up at this time, he insists that you must have been confused, maybe in the past he got off work early once but he definitely always just comes home at this time
You wonder if you’re really that unobservant. Honestly, that is so like you to be kinda airheaded. You’re not too smart, or you’d know for sure what time he gets home. The fact that you doubt it is not a good sign, he seems pretty sure that he always got home at this time. You shrug. You move on. He goes on screwing the secretary. Some day you find a pair of underwear in your laundry and it’s not yours. You ask him about it. He says he got you those two years ago for your anniversary, what the fuck, why don’t you remember? You apologize because you feel bad for being inconsiderate, forgetting something that mattered to him. You wear the women’s underwear to dinner as a make-up surprise.
It’s beyond simple lying, it’s lying that makes you doubt your reality and makes you docile, easy to control because you no longer trust which way is up, you have to depend on them to tell you which way is up.