All the refs make it look territorial, but I'll accept those quotes.

@@ -21,0 +21,1 @@
+<gloss>grounds (e.g. school)</gloss>

Although I believe this word often has more military or feudal overtones, it appears it can also be used for the "grounds" of a school or estate, as in 学校の領地. Here are a couple examples I found online:

今日も僕たちの学校の領地内で勝手に測量を始めたよ。

月夜の晩、学校の領地全体に警報が鳴らされた。

Although "territory" covers the same idea, "grounds" is how I would more commonly expect to see it in English.