Gaslighting is a colloquialism, loosely defined as manipulating someone into questioning their own perception of reality. The expression, which derives from the title of the 1944 film Gaslight, became popular in the mid-2010s. Merriam-Webster cites deception of one's memory, perception of reality, or mental stability. According to a 2022 Washington Post report, it had become a "trendy buzzword" frequently used to describe ordinary disagreements, rather than those situations that align with the word's historical definition.

Gaslight is a 1944 American psychological thriller film directed by George Cukor, and starring Charles Boyer, Ingrid Bergman, Joseph Cotten and Angela Lansbury in her film debut. Adapted by John Van Druten, Walter Reisch, and John L. Balderston from Patrick Hamilton's play Gas Light (1938), it follows a young woman whose husband slowly manipulates her into believing that she is descending into insanity.