noun, の adjective
This is my territory. This is my region. This is my domain!
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
It is better to clarify the boundaries of each area.
This is no longer within the realm of science.
Everyone has to take a step into unknown territory to progress.