-(으)ㄴ/는데 is used when the first clause expresses the reason or background situation for the second clause and also when the first clause provides content introducing the second clause. It corresponds to 'so/therefore' and 'and' in English. When added to adjectives, -ㄴ데 is added to stems ending in a vowel, and -은데 is added to stems ending in a consonant. When added to verbs, -는데 is added to the stem.

Kimchi Reader

Used by the speaker to provide some background information to the listener so they can understand the context.