How would you translate 란/이란 in English?

란/이란 is a topic marker similar to 은/는 that attaches to nouns, but is more emphatic than 은/는. It is an abbreviation of (이)라는 것은. The marker 란 attaches to nouns that end in a vowel (eg. 친구란), and the marker 이란 attaches to nouns that end in a consonant (eg. 가족이란).

The marker essentially announces that you are about to define or explain the noun to which it is attached, as the following example shows.

친구란 어려울 때 도와줄 수 있는 사람이에요.

A friend is someone who helps you in difficult times.

Dictionaries often show "as for" as an English equivalent of 란/이란, but normally we would not translate it in English. However, in spoken English, we usually show the emphatic nature of the marker by stressing the noun to which 란/이란 is attached and then pausing before continuing on with the definition or explanation of the noun, as demonstrated below:

A friend--is someone who helps you in difficult times.

In the above example, the boldface type is meant to indicate stress, and the hyphens (dash) are meant to indicate a pause.

Normally, Koreans also pause after the marker 란/이란 before continuing on with the definition or explanation of the word or phrase to which it is attached.