< Latin līmin-, līmen threshold + -al suffix1.
a. gen. Of or pertaining to the threshold or initial stage of a process. rare.b. spec. in Psychol. Of or pertaining to a ‘limen’ or ‘threshold'. (OED)
"As you point out, the story ends with Yunior about to turn forty, which is a very liminal place to be, especially for an immigrant dude like him. It’s one thing to be an immigrant ten years out from arrival and quite another to be an immigrant thirty years out from arrival. When I was a young I always thought I would reach a point where my immigrant-ness would suddenly fall away, and I would miraculously become an American. Now I know that’s not what happens: being an immigrant is one of those things that is forever."
- Junot Díaz, "This Week in Fiction: Junot Díaz", Page-Turner 16 July 2012
No, I'm still not sure what he means.