A secret crush is someone you only meet once but they make such an impression that you never forget about them. Eventually, you develop a crush on the idea of them and long for the relationship you imagine in your head.
Originally coined on the show How I Met Your Mother in the episode "Hopeless."
Robin: “Oh, my god! My secret crush is here!”
Lily: “Mila Kunis?!”
Robin: “No, MY secret crush. We met a few years ago. . . . I had to leave before we finished talking so that was it. You know, ever since then, I’ve always… Oh, my god, he’s coming over!“