the open belt of land that rings a town: its commons for grazing, kept free of building
Migrash is the ring of open ground that surrounds a settlement. It is the land just outside the wall, left unbuilt and unfarmed so the townspeople could pasture their flocks and herds there, store goods, and have room to breathe. The word almost always travels in a fixed pair with "cities": the towns and their open land, the built place and the green belt around it.
The heart of the word is the law that gave the Levites no tribal territory of their own but assigned them towns scattered through Israel, each town wrapped in this open commons. Numbers 35 even measures the belt out, a fixed distance running out from the wall on every side, and the long town lists of Joshua 21 and 1 Chronicles 6 repeat the phrase town after town like a refrain. So the word carries a settled, legal flavor: it names a defined zone with a defined purpose, not just any empty field.
The same picture stretches naturally to the open space ringing other built things. Ezekiel measures a margin of open ground around the future temple and around the holy city the same way Numbers measured it around a Levitical town. The constant is the shape: a girdle of cleared, common land hugging something built.