Ecotone
Etymology
Coined in ecology around 1904 from the "eco-" of "ecology" (Greek "oikos," "house, dwelling") and Greek "tonos" ("tension"): literally a zone of tension between communities. Such edges often teem with species from both sides plus some found only there.
noun · /EE-koh-tohn/
The transition zone where two ecosystems meet and blend, often unusually rich in life.
What it names
A precise word for productive borderlands — the edge between forest and meadow, land and sea — and a fine metaphor for the fertile overlap between two worlds.
Example
The neighborhood was a cultural ecotone where two immigrant communities overlapped and something new grew in the seam.
Related idea
Compare the human-centered liminal, a threshold state of being betwixt-and-between; an ecotone is the physical, living edge itself, prized precisely for what thrives in the overlap.