Used to convey information heard from someone else; 'I heard', 'They said'.
The ～んだって grammar point is used to convey information that the speaker has heard from someone else. It can be seen as the combination of explanatory のだ (んだ) and the informal quoting particle って. It can be translated as 'I heard' or 'They said' in English. The formation differs depending on whether it is used with a verb, い-adjective, な-adjective, or noun.