Simple Definition:

Gaslighting is a form of psychological manipulation where someone tries to make another person doubt their reality (make someone question what they believe is true). This can involve lying, denying, or distorting facts to gain control over the victim. For example, if someone repeatedly tells their partner that they are forgetful or crazy when they remember things correctly, it is a form of gaslighting.

Very Simple Definition:

Gaslighting is when someone tries to make another person doubt what they know is true. For example, if someone keeps telling their friend that they never said something, even though they did, it is gaslighting.