You can think of a check-in as the moment of saying “I'm here” to whoever is keeping track. You arrive, you make yourself known, and something of yours passes over — your name, your ticket, your bags, your news. After that moment you are in the system: the desk knows you, the app knows where you are, the team knows what you have done. The word can name that moment, the place where it happens, or one single record of it.
From the word’s history
Wiktionary records check-in as deverbal from the phrasal verb check in: the action came first, and the noun is that action picked up whole and used as a thing.
Wiktionary 記的是 check-in 由動詞片語 check in 直接轉成名詞。可以想成先有「報到」這個動作，再把整個動作拿起來當成一樣東西來講。所以它才能同時指那個動作、做這個動作的地方，以及留下來的一筆紀錄。
Wiktionary (kaikki snapshot 3f6f69a190036ae4, source_ref kaikki:3f6f69a190036ae4:1396372127), check-in etymology: “Deverbal from check in.”
登入就可以看每一支怎麼連回核心畫面。