The concept that exists just to make people in Algebra 2 die of confusion.

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.

a person you meet once in your lifetime when on vacation, but when the vacation is over you continue to keep in constant contact with each other via text, facebook, e-mail, post, phone calls, or all of the above.

A friend that only appears to you and you only, you can play around with the friend but sex is not possible.

>The square root of a negative number.
>A number which you can think of which doesn't actually exist.

A constant companion that nobody can see except children and the religious.

Claiming to have had sex when none of your friends believe you.