Refers to information that comes through informal channels, like gossip or something heard through the grapevine. Often used in the phrase 風のつてに聞く (to hear through the grapevine).
See also: 風の便り (かぜのたより)
I heard about his marriage through the grapevine.
Rare kanji spelling; 伝 is not commonly used for this word.
Compound of 風 (kaze, 'wind') + の (no, possessive particle) + つて (tsute, 'means, connection'). The word つて originally means 'connection' or 'introduction', and the phrase evokes news carried by the wind.