Learn Hardcore Korean: daegi junge mesijireul bonaesseoyo.

대기 중에: Literally “during standby/waiting.” Slightly clipped/technical; common in UI or status-like language, but perfectly acceptable in normal speech.
기다리는 동안(에): “While/for the duration of waiting.” Neutral and very natural in everyday conversation; emphasizes the time span.
기다리면서: “While waiting (and doing something else).” Stresses simultaneity of two actions; casual and dynamic.

Examples:

대기 중에 메시지를 보냈어요. (neutral, a bit status-like)
기다리는 동안(에) 메시지를 보냈어요. (very natural)
기다리면서 메시지를 보냈어요. (casual, concurrent actions)

Is 대기 the natural word for “wait,” or should I use 기다리다?

대기: Sino-Korean; often sounds formal/technical (“on standby,” “in queue,” systems/announcements). Very common in phrases like 통화 중, 대기 중, 사용 중.
기다리다: Native verb; the go-to choice in everyday conversation for “wait.” So in casual speech, 기다리다 (or 기다리는 동안/기다리면서) often sounds more natural than 대기 중에.

Why is there a space in 대기 중에 and is 대기중에 wrong?

중 is a dependent noun (의존 명사), so it is written separately from the preceding noun:

Correct: 대기 중에 (대기 + 중 + 에)
Nonstandard in formal writing: 대기중에 You’ll see no space in UIs or signs (대기중), but standard spacing for prose is 대기 중 / 대기 중에.

What’s the difference between 중 and 중에 here?

N + 중 + 이다: “to be in the middle of N.” Example: 대기 중이에요. (“I’m waiting/On standby.”)
N + 중에: “during N.” Example: 대기 중에 메시지를 보냈어요. (“I sent a message while waiting.”) 중 by itself describes a state; attaching 에 makes it an adverbial time phrase (“during”).

Can I drop 에 and say 대기 중 메시지를 보냈어요?

In everyday speech, that sounds odd. Without 에, 대기 중 tends to modify a noun in clipped written styles (e.g., 안내문, UI), not function as “during.” Use 대기 중에 for “during.” Keep 에 here.

Where can I place 대기 중에 in the sentence?

It’s flexible, but sentence-initial feels most natural:

대기 중에 메시지를 보냈어요. (most common)
메시지를 대기 중에 보냈어요. (acceptable, emphasizes the timing) Avoid splitting the phrase; keep 대기 중에 together.

What politeness level is 보냈어요, and what are alternatives?

보냈어요: Polite informal (해요체), past. Alternatives:
보냈습니다 (formal polite)
보냈어 (casual intimate)
보냈다 (plain/written/diary style)
보냈네요 (polite with a nuance of realization)

Do I have to keep the object particle 를 in 메시지를?

No. Object markers are often dropped in speech if the meaning is clear:

메시지(를) 보냈어요. (both fine) Keep 를 if you want clarity or emphasis, especially in longer sentences.

Is 메시지 the best word here? What about 문자 or 카톡?

메시지: General “message” (any platform).
문자(메시지): Specifically “text/SMS.” Often just 문자.
카톡: KakaoTalk message (very common in Korea). Example: 카톡 보냈어요. Use the one that matches the channel you mean.

Is 메세지 a misspelling?

Yes. The standard spelling is 메시지. 메세지 is common informally but considered nonstandard in careful writing.

Can I say 기다리던 중에 or 대기하던 중에 instead?

Yes. 던 marks an action that was in progress at that time:

기다리던 중에 메시지를 보냈어요. (very natural: “While I was in the middle of waiting…”)
대기하던 중에… (more formal/technical flavor) You’ll also hear 기다리는 중에 in real usage; both -는/-던 + 중에 occur.

How does -면서 compare? Can I say 기다리면서 메시지를 보냈어요?

기다리면서 메시지를 보냈어요 is natural and emphasizes two simultaneous actions by the same subject.
대기하면서 is grammatical but sounds more formal/technical than 기다리면서 in daily conversation.

How do I say “while waiting for my friend/the bus”?

Use 기다리다 with the object:

친구를 기다리는 동안(에) 메시지를 보냈어요.
친구를 기다리던 중에 메시지를 보냈어요.
버스를 기다리는 동안(에) 메시지를 보냈어요. Avoid attaching an object directly to 대기 중에; use 기다리다 for “wait for (someone/something).”

Could 대기 mean “atmosphere (air)” and be confusing?

대기 does also mean “atmosphere,” but context disambiguates it. In set phrases like 대기 중(에), it virtually always means “standby/waiting,” not “in the atmosphere.”