Usually as a result of not having much or any friends in reality, your mind creates an imaginary friend. Even the creator of an imaginary friend cannot see them, unless if they are on LSD, or just hallucinogenic. You're not nessecarily "crazy" if you have one.

You can just talk to them in your mind, they can think for you sometimes, you can ask them for advice or ask them to decide which movie you want to rent tonight. You can get into arguments with them, and you can have intelligent conversations with them.

But...

You can't kill them.

They might slowly fade away in time... but... I don't know...

Yeah.

Also.

You can completely change into your imaginary friend. Sad I know.

A phrase to describe someone who is cognitively degenerating. Synonym of "going off the deep end". Can have varying degrees of severity.

Reference to the song "Hey You" by Pink Floyd. The line "and the worms ate into his brain" makes no sense in an otherwise linear and literal narration throughout the lyrics.

A "character" created by the imagination to keep a person company. Sometimes, it can be difficult for the person to recognise that their "friend" is not real; at other times, they can be recognised as not being real, but are still used to offer comfort and company.

An imaginary friend is NOT the result of mental impairment. Actually, those with an imaginary friend are frequently smarter than most people (two brains in one). It's someone who is always with you, thus you are never alone. He knows you, your greatest desires and your flaws. So he usually judges you... but also the others around you. He comes often when you feel alone and need some help, or need to talk but have nobody trustworthy. An imaginary friend is really helpful, I advise you to try ! But pay attention, if your friend is comic, to not laugh too loud. People could think you're strange, even if it is a good thing, they're not really tolerant.

PS : Never let someone tell you he is not real, “Of course it is happening inside your head, but why on earth should that mean that it is not real?” (JKR)

a living person who you talk to constantly but never see them.

A person or whatever it may be that you become friends with but no one else can see. The most common name for an 'imaginary friend' is Bob.

A figment of the imagination usually made up by little kids who dont have many friends or have a hard childhood life. Or by some insecure teenagers who have to pretend they have friends to impress people. Also made up by insecure friendless adults who pretend like they go out with someone when its all imaginary and made up in thier head.