The noun שדה (field) in its precise meaning is a field of only seeds. And in its broad meaning, it also includes a place of trees.

השדה is in the middle, between a city and a desert; and thus, it is used to speak by way of metaphor for any intermediate matter, as it does with a private altar⁷¹⁸ (which is in the middle, between the Temple in Jerusalem and the Tabernacle in the desert), in the learning of the Mishnah (which is in the middle, between the Scripture and the Gemara), about a young girl who is engaged (who is in the middle, between a single girl and a married woman): The young girl who is engaged is referred to with the noun שדה opposite of the poetic language to call a woman with the noun אהל (tent) or the noun בית (house); thus, the sages of blessed memory interpret וישב מחוץ לאהלו (but shall dwell outside his tent)⁷¹⁹ to be about permitted relations.

footnotes: ⁷¹⁸ Leviticus 17:5. There it refers to a private altar with the language על פני השדה (in the open field). ⁷¹⁹ Leviticus 14:8.