If you hear some news or information on or through the grapevine, someone else tells it to you unofficially, often in conversation.
EXAMPLES:
"Who told you I was moving house?" "Oh, I just heard it on the grapevine."
Freddie was distressed when, through the grapevine, he heard of Liza's marriage.
I heard through the grapevine that she was pregnant, but I don't know anything more.
According to the high-school grapevine, Kelly wants me to ask her out on a date.
