Picture the ground just behind a house: you step out of the back door and you are standing on it, you can cross it in a few seconds, and it belongs to the people who live there. Two things are true of that ground at once — it is the nearest outdoor place to you, and it is yours. Every other use of backyard can be seen as those two feelings carried onto something much bigger than a yard.
The word is put together from back and yard: yard gives the fenced-off piece of ground, back says which side of the house it is on.
這個字由 back 加 yard 組成。yard 給的是「圍起來的一塊地」，back 告訴你在房子的哪一邊。合起來就是字面上的「後面那塊圍起來的地」，而這正好就是核心畫面本身。
Wiktionary entry for backyard (kaikki:3f6f69a190036ae4:1158416965:23066), etymology_text: 「From back + yard.」
Three branches
房子後面的那塊地
這一組就是核心畫面本身，只是英美看到的地面不一樣。位置一樣在房子後面，差別在那塊地是草還是水泥。
noun · A2
The piece of ground directly behind a house, belonging to the people who live there, often covered with grass and used for growing things, eating outside, or letting children and pets play.
後院
離我很近、算我地盤的那一片
把核心畫面的圍牆拿掉，只留下「就在旁邊」和「算我的」這兩個感覺，再放到更大的地方上。地方變大了，語氣還是同一種。
noun · B2
The area around where someone lives or works, spoken of as the place they know well and treat as their own, even though it is much bigger than a real yard.
地盤、常走的那一帶
固定說法：就在自家後院
這兩句把後院當成一條線來用：線外的事是別人的事，線內的事就是我的事。整句意思屬於整個說法，不是 backyard 單獨帶著的。
noun · B2
Used to say that something is happening very close to where a person lives or works, so it affects them directly instead of being a distant matter.
就在自家門口