You can think of a lock-up as a small space with a door that locks, holding whatever has been shut inside it. The picture stays the same and only the contents change: a person waiting overnight at a police station, or a bicycle and a toolbox behind a row of flats. Either way it is small, it is separate from ordinary life, and the lock is the point of it.
可以想成 lock-up 就是「一個上了鎖的小空間，裡面關著被鎖進去的東西」。畫面一直沒變，變的只是裡面裝什麼。有時候關的是人：在警局待一個晚上，等隔天上法庭。有時候關的是東西：公寓後面那排小車庫裡的腳踏車和工具箱。兩邊都一樣小、都跟日常生活分開，而且那把鎖就是這個字的重點。
From the word’s history
Wiktionary records lock-up as a deverbal noun from the phrasal verb lock up, so the noun simply names the place where something is locked up.
Wiktionary 記 lock-up 是從動詞片語 lock up 直接轉成的名詞，所以這個名詞就是在指「把東西鎖起來的那個地方」。
Wiktionary entry for lock-up, etymology_text: Deverbal from lock up (packet ref kaikki:3f6f69a190036ae4:2252129314)
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