Weird is a wayward word: though it describes a set of singular effects that link the cultural fringe with peculiar personal experiences, it remains an elusive and marginal term. The similar notion of the uncanny is, on the other hand, basically an establishment term, a well-established literary effect with a sophisticated psychoanalytic pedigree. Weirdness, we might say then, is the uncanny's low-brow doppelganger, a demotic country cousin that races hot-rods, wears mis-matched socks, and inhabits the strange borderlands between this world and the beyond.

The roots of weirdness lie in the noun wyrd, an Old English term that pops up in Beowulf and denotes the (usually grim) demands of destiny. The adjective first appears in the phrase weird sisters, which was used by Scottish poets to describe the classical Fates before Shakespeare attached the term to the witches of Macbeth. But Shakespeare's spelling of weird is, well, a bit weird—"weyrd", "weyward", and "weyard" appear in the first folio, but never "weird". These alternate spellings, again, suggest the term wayward, a word used by Shakespeare to denote the capricious refusal to follow rule or reason. This suggests to some Macbeth scholars that, in addition to their oracular knowledge, the witches are also defined by their willful resistance to the norm, a perverse and chaotic twist away from the law. Early on, then, weirdness already covers two contrasting but related forces: necessity and anomaly.

The eerie aesthetic of weirdness bloomed in the hands of the Romantics, with Shelley comparing himself in one verse epistle to "some weird Archimage…plotting dark spells, and devilish enginery". Besides using the term in this atmospheric sense, Shelley also linked it with a certain kind of story, as when, in "Witch Atlas", the poet speaks of a "tale more fit for the weird winter nights / Than for these garish summer days." In this sense, "weird" not only describes the witches in Macbeth, but Macbeth itself, a supernatural or weird tale whose telling is realized through the "devilish enginery" of text and stagecraft.

Weirdness loomed even larger in the popular genre of the Gothic novel, whose chart-topping tales of ghosts, aberrant sexuality, and religious exotica eventually led to the modern genre of supernatural horror. By the early twentieth century, some writers and critics started referring to such dark fantasies as the "weird tale," and in spring 1923 the fantasy magazine Weird Tales launched, and was soon serving up macabre wonders by Robert E. Howard, Clark Ashton Smith, and, of course, H.P. Lovecraft. In his essay on supernatural horror, written around the same time, Lovecraft stressed that weirdness was at once an emotional, imaginative, and cognitive effect. "The one test of the really weird is simply this—whether or not there be excited in the reader a profound sense of dread, and of contact with unknown spheres and powers…" Some weird stories introduce only a single supernatural or anomalous element, while others elaborate fantastic and unreal worlds that, when they work, accord with what Lovecraft believed were the human brain's innate imaginative capacities. But for Lovecraft himself, the most powerful weird tales should be rooted in naturalism, devised, as he famously wrote to Smith in 1930, "with all the care and verisimilitude of a hoax."

The downward drift of the weird—contrasted again with the fancy-pants frisson of the uncanny—landed it by mid century in the lower realm of exploitation movies, Mad magazine, Kustom Kar Kulture, EC comic books (with their Weird Science and Weird Fantasy titles), and other unserious outposts of horror, macabre fantasy, and science-fiction. Weird culture was greasy kid stuff, with an aberrant or even "delinquent" profile that played well with social outsiders. Teenagers, hot-rodders, bohemians, drug users, underground comics artists, and odd-balls of all stripes took up the flag of the weird or found it draped upon them—since the 1940s at least, "weirdo" has denoted not only threatening (and possibly perverted) individuals, but those who are merely, even self-consciously peculiar.

By the closing decades of the twentieth century, the culture of weirdness had largely drifted away from the oracular or supernatural, away even from the spine-tingling atmospheres of the eerie, and towards a sort of trashy, pop-culture alterity. Take R. Crumb's Weirdo magazine, which ran from 1981 to 1993 as an intentionally "low-brow" compendia of underground comix, outsider art, frank quotidian tales, and Church of the SubGenius-style agitprop clearly aimed, like Rev. Ivan Stang's High Weirdness by Mail, at fellow "weirdos."

And yet: the sacred trace remains. Even in the most low-brow drive-in monster mash, weird culture generates a highly ambivalent blend of wonder and horror that recalls the famous definition of the numinous provided by the religious historian Rudolph Otto in The Idea of the Holy, where he described the sacred Other as mysterium tremendum et fascinans—a mystery that at once repels and attracts, terrifies and fascinates. Otto's distinction also informed the religious historian Mircea Eliade's influential notion of the paradoxical relationship between the sacred and profane. For Eliade, the sacred is a higher ontological realm, but it can manifest in just about anything on the profane plane—and especially strange things. "Everything unusual, unique, new, perfect or monstrous at once becomes imbued with magico-religious powers" he wrote. Here we once again find a key element of the weird, an element whose best name—at once technical and evocative—is anomaly.

Whether or not it may seem supernatural, the anomalous appears as nothing more or less than a deviation from the norm: an unknown object moving at right angles in the sky, or a synchronistic string of the same apparently random number popping up. (Of course, what constitutes a meaningful anomaly is another question.) But as culture-makers know, weird anomalies can also be produced. For example, when the anthropologist Bronislaw Malinowski analyzed the traditional magic workers of the Trobriand Islands, he identified what he called the "weirdness coefficient" of their spells. This coefficient—in mathematics, the term means a fixed multiplicative factor—was composed of secret names, "abracadabra", unusual phonetic combinations, alliteration, "weird cadences," and other statistical deviations from ordinary colloquial language. Such wayward moves not only helped produce the otherness and social power of magical speech, but suggested that weirdness could be quantized as a measure of deviant deviation. Today some linguists have attempted to rigorously quantify the "weirdness coefficient" within the computational context of natural language processing, which demands the ability to gauge potentially meaningful statistical variances in vast arrays of linguistic values.

Weirdness, then, serves up the ambivalence of the anomaly: a deviation from the norm intense enough to undermine naïve realism, but not so much as to invoke the otherworldly. This perhaps helps explain the term's parallel life in popular discussion of quantum mechanics, a discourse that was launched when the physicist Heinz Pagels peppered his popular 1982 book The Cosmic Code with the phrase "quantum weirdness." Weirdness, in this sense, stands for experiences or events that seriously challenge the norm without leaving the empirical plane of immanence. The weird twists, but does not transcend. It doesn't rupture reality but refers, enigmatically, to its perverse core. Even as the weird retains an aura of the sacred, this glow is folded into the profane, a centrifugal or wayward turn away from naturalistic norms to which it remains, nonetheless, intimately tied.