Despite our best efforts, humans aren't always the kindest to each other, and one of the most common forms of mental and emotional abuse we put each other through is gaslighting. In short, gaslighting is a form of manipulation where someone denies your experiences and your perception, essentially making you doubt your own reality. People who gaslight do so to try and remain in control of situations where they feel they have no control, but it can be incredibly dangerous on a psychological level.
The term gaslighting comes from a 1938 play in which a husband slowly convinces his wife that she is crazy. He does this by making slight changes to their home and then denying them when she points them out. The biggest change that he makes is dimming the gas lamp in their house - hence the term gaslighting.
Gaslighting is essentially any sort of manipulation designed to make you doubt your own perception. People do this all the time - in relationships, at work, in social situations. Some forms of gaslighting are so mild you probably don't even notice them. For example, a salesperson in a clothing store trying to convince you that you can't live without a product is a common form of gaslighting, because it starts to make you doubt that you can continue on in your life without the product.
There are many reasons why gaslighting is very dangerous. It's particularly harmful in any close relationship, like a friendship or a romantic relationship, or in a situation where one person has power over the other, like a boss-employee relationship. Since gaslighting makes the victim doubt their perception of reality, it makes them much less likely to stand up for themselves in a situation where they are being abused. This can lead to very intense emotional trauma and even physical abuse in some cases.
While you can't stop other people from gaslighting, there are things you can do that will help you better identify it and avoid it. For example, if you feel like you are being gaslit, try to remove yourself from the situation and then assess it from a neutral perspective. Ask for a third party perspective if you are still unsure of what to do or where to go from here.
If you feel you are being gaslit, it also may help to see a therapist, either on your own or with the person who is gaslighting you. Couples therapy can be a very useful solution if this is happening in a romantic relationship. Your therapist will act as a neutral third party so you won't have to worry about the gaslighter taking total control of the situation. However, if you feel that someone is consistently gaslighting you, you should make a concerted effort to exclude them from your life. A gaslighter is not someone you can reason with, and the best way to avoid their negative behavior is to stay away from them.