What's This...

1.X is a word coined in 1931 by American writer Charles Fort to describe the strange disappearances and appearances of anomalies, which he suggested may be connected.Similar is apport, an earlier word used to describe what today might be called X; and bilocation, when something or someone described as being a magician is said to be able to occupy two places simultaneously. Fort's first formal use of the word was in the second chapter of his 1931 book, Lo! "Mostly in this book I shall specialize upon indications that there exists a transportory force that I shall call X." Though, with his typical half-serious jokiness, Fort added, "I shall be accused of having assembled lies, yarns, hoaxes, and superstitions. To some degree I think so, myself. To some degree, I do not. I offer the data."

What's X?