이란: The Thing Called — Pinning a Topic for Definition

이란 (and 란 after vowel-final nouns) picks a noun out and puts it on the table as the thing we are talking about — often so you can define or judge it.

Curriculum gloss: the thing called — introducing a definition. 우리말샘 treats 이란 as a particle after batchim nouns that specially singles the referent out as topic. Classroom Korean leans hard into the …이란 …이다 definition frame.

Attachment

좋은 숙소란 깨끗하고 조용한 곳이다.
우정이란 어려울 때 돕는 것이다.
여행이란 계획을 세우는 것부터다.

Do not write *친구이란. That is the batchim form forced onto a vowel stem.

Not plain 은/는

은/는 vs 이/가 marks ordinary topics and contrast. 이란 still topicalises, but the flavour is “as for what we call X…” — definitional, evaluative, proverb-adjacent.

숙소는 비싸요.              plain topic: the lodging is expensive
숙소란 편해야 한다.         framed judgment: lodging (worth the name) should be comfortable

English as for / the so-called sometimes overlaps, but Korean 이란 is not sarcasm by default. Sarcasm needs tone and lexis.

Versus 이라고

Same unit teaches 이라고. Keep the jobs apart:

그 호텔이란 가성비가 좋은 곳이다.     framing what ‘that hotel’ amounts to
그 호텔이라고 예약했어요.             naming / quoting the label

Lodging-unit feel

Travel Korean loves definitional openers when people argue criteria:

가성비란 가격 대비 만족도이다.
조용한 숙소란 밤에 잠이 잘 오는 곳이다.
리뷰란 참고만 하는 것이다.

Pair with 이다 for the classic N이란 …이다 close.

Quick checks

1. Batchim → 이란; vowel → 란.
2. Use it to frame what X is / should be, not as a drop-in for every 은/는.
3. Do not confuse country-name 이란 with the particle — Hangul collision, different word.

Ask: am I defining or judging what this noun amounts to? If yes, 이란 fits. If you are only marking a plain topic, stay with 은/는 vs 이/가.