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.
可以想成房子後面那塊地：推開後門就踩在上面，走幾步就走完，而且只有住在裡面的人在用。這塊地同時有兩個特點——它離你最近，而且它算你的。backyard 後面長出來的其他用法，多半就是把這兩個感覺搬到比院子大得多的地方去用。
From the word’s history
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.」
登入就可以看每一支怎麼連回核心畫面。