The concept's hardening can be dated with unusual precision to two texts. Arnold van Gennep's Les rites de passage (1909) proposed the threshold, or liminal, phase as the middle term of separation, transition and incorporation; the book had little immediate impact and was not translated into English until 1960. Victor Turner's The Ritual Process (1969) then supplied the vocabulary now in general use, developing communitas for the levelled fellowship of those inside the liminal phase and giving the concept the theoretical weight it carries today.
Turner himself extended the term outward in a 1974 essay proposing "liminoid" for the voluntary, individual analogues of liminality found in industrial societies, theatre and art, as against the obligatory liminality of small-scale initiation that one cannot opt out of. That extension is the beginning of the concept's drift toward looser modern usage.
The drift has continued well past Turner's own caution. "Liminal space" and "liminality" now circulate widely in organisational consulting, design writing and popular psychology to describe almost any period of uncertainty or transition, a usage scholars of ritual generally regard as diluted past the point of analytical use. A partial parallel exists in Islamic thought's barzakh, the intermediate state or barrier between two conditions, most often discussed as the interval between death and resurrection; the resemblance is suggestive rather than a claim of shared origin, since the two concepts developed independently in unrelated textual traditions.