ELI5: Explain Like I'm 5

Invisible Pink Unicorn

An invisible pink unicorn is an imaginary creature, like a unicorn (which is a horse-like animal with a single horn in the middle of its forehead). The difference is that this unicorn isn't visible to the human eye. It is like a mysterious mythical creature that only a few people might believe in, but nobody can see it or know what it looks like.