Picture a machine that has stopped. The clock keeps running, but nothing is being made. Downtime is that stretch of empty time — the hours when the thing that should be going is not going. What has stopped can be a server, a factory line, a whole business in its quiet month, or a person who has finished what they were doing.
可以想成一台機器停了下來。時鐘還在走，但東西沒有在做。downtime 就是中間空掉的那一段時間——該動的沒有在動。停下來的可以是伺服器、產線，也可以是淡季裡的一整間店，或是手邊事情做完的人自己。
From the word’s history
Wiktionary records the word as down (out of order; out of service; inoperable) + time, which is exactly the picture: the time during which something is down.
Wiktionary 記的組成是 down（停擺、不能用）加 time。這正好就是那個畫面：某樣東西 down 著的那段時間。
Wiktionary entry for downtime, etymology_text: From down ("out of order; out of service; inoperable") + time.
登入就可以看每一支怎麼連回核心畫面。