What is gaslighting? The 1944 film Gaslight is the best explainer.

It’s just as chilling today as it was back then.

Every weekend, we pick a movie you can stream that dovetails with current events. Old, new, blockbuster, arthouse: They’re all fair game. What you can count on is a weekend watch that sheds new light on the week that was. The movie of the week for January 21 through 27 is Gaslight (1944), which is available to stream on Filmstruck or digitally rent on Amazon, YouTube, iTunes, Google Play, and Vudu.

The term “gaslighting” has gotten thrown around a lot over the past year, mostly in reference to political campaign tactics — when candidates claimed something had (or hadn’t) happened, and refused, when confronted with contradictory evidence, to acknowledge otherwise. Lauren Duca most famously wrote about the term for Teen Vogue in a piece titled “Donald Trump Is Gaslighting America,” for which she caught some heat and also raised the profile of Teen Vogue.

But as with most terms that quickly become popular, a lot of people don’t know what it really means. Does it just mean deceiving people? Or is it something more specific?

You could look up definitions, but the best way to understand gaslighting is to go to the source. George Cukor’s Gaslight — based on a 1938 play by Patrick Hamilton — stars Ingrid Bergman as a naive, sweet young woman named Paula who as a young girl witnessed the murder of her beloved aunt (and guardian) at their home. Years later, in Italy, she meets and marries dashing Gregory (Charles Boyer), who returns with her to London to live in the house she inherited from her aunt, which is also the house where the murder occurred.

But slowly, over time, Paula begins to doubt her sanity. Gregory tells her that she’s becoming forgetful and fitful, acting in irregular ways. He confines her to the house, and tells everyone she’s not well. At night she hears knocking in the walls. She sees the gas lighting dim. But he tells her she’s imagining things.

The film also features Joseph Cotten as a detective who begins to suspect that something’s up, and Angela Lansbury as the saucy housemaid. It was nominated for seven Oscars in 1945 (including Best Picture and Best Adapted Screenplay).

And while I find the film’s ending unsatisfactory — it lets Gregory off the hook by painting him as less of a sociopath and more of a very determined and innovative thief — the scenes in which Gregory is flat-out lying to Paula, coolly watching her come to pieces, are utterly chilling. It’s abuse, and an insidious kind, since the abuser doesn’t leave any marks.

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.

The trope has been repeated throughout film history (The Girl on the Train is a great example), but Gaslight still holds up — especially in a week where people are throwing around terms like “gaslighter-in-chief” to describe the newly inaugurated president. And if you can stomach watching Gaslight, it’s a useful reminder that just because you feel like you’re going crazy doesn’t mean you are.

Watch the trailer for Gaslight: