Use the adjective unconfirmed to describe something that may or may not be true. If you've heard that there might be a pizza party at school tomorrow, but it hasn't been officially announced, it's just an unconfirmed rumor.
You'll probably come across this word if you spend much a lot of time reading or listening to the news. Unconfirmed reports of a suspect running west down Main Street mean that there's been chatter about seeing this person, but no one can or establish the truth of the sighting. Unconfirmed things haven't been photographed or filmed, and they don't have an authority declaring them to be fact.