What's a liminal?

lim·i·nal
ˈlimənl/
adjective
Latin limin-, limen, threshold

    1.    of or relating to a transitional or initial stage of a process.
    2.    occupying a position at, or on both sides of, a boundary or threshold.
    3.    in biology, liminal can refer to edge habitats - areas where two habitats meet, such as field and
           forest, ocean and land.

Liminal can refer to both physical places and living beings.
It's one of the main concepts that Edge the novel is built around.
During liminal times, social structure often crumbles, traditions break down, and there's a lot of doubt and uncertainty about how the future will turn out (sound familiar?).
But the crumbling of all these solid "structures" causes everything to become more fluid... sort of like  ice melting into water. Transformation requires destruction... things need to become fluid in order to change.
Liminality enables new structures, societies and customs to form.

"Edges are all about rapid and extreme change – only certain hardy lifeforms can survive there."
~ Rachel Carson