liminal

adjective4

1. •
   Of or pertaining to an entrance or threshold.
2. •
   Pertaining to or in a state that is in-between or transitional between two (or more) other states, while belonging to neither; pertaining to or in a state such as to be neither definitively in a particular other state or category nor definitively outside it.
3. •
   (informal) Of an empty environment that evokes a surreal blend of nostalgia, comfort, and unease; see liminal space.
4. •
   Of or pertaining to a beginning or first stage of a process.

   • Every stimulus must reach a certain intensity before any appreciable sensation results. This point is known as the threshold or liminal intensity. — 1884