Gaslighting is a form of psychological manipulation in which the manipulator tries to make the victim doubt their own perceptions and memories. The manipulator does this by denying that certain events occurred, manipulating evidence to support their own version of events or even planting false memories in the victim's mind.
This buzzword that is so often used to describe certain situations usually leaves the victim feeling confused, uncertain, and dependent on the manipulator. This can be extremely damaging to the victim's mental health and can lead to feelings of low self-esteem and a lack of trust in their own judgment.