Hear through the grapevine Informal

To learn news or information through informal, unofficial channels — gossip, rumor, or word of mouth — rather than a direct or authoritative source.

It usually comes with an implicit caveat that the information might not be fully accurate, since it passed through several people before reaching the listener.

The phrase is generally traced to the telegraph systems built during the American Civil War (1861-1865): wires were often strung loosely between poles over long, improvised stretches, visually resembling the trained vines of a vineyard, and messages sent over these makeshift lines were frequently garbled or unreliable, unlike the more accurate official telegraph reports. “Grapevine telegraph” became a term for this kind of unofficial, distorted communication network, and it shortened over time into simply “the grapevine.” The expression’s modern popularity owes a great deal to a 20th-century cultural artifact separate from its 19th-century origin: the 1966-67 Motown song “I Heard It Through the Grapevine,” recorded by both Gladys Knight & the Pips and, more famously, Marvin Gaye, which became a number-one hit and permanently cemented the phrase in everyday English.

I heard through the grapevine that they’re moving to Berlin.

She heard through the grapevine about the layoffs before the announcement.

Don’t believe everything you hear through the grapevine.

A: “How did you find out about the wedding?” B: “I heard it through the grapevine.”