Credence means truthfulness, or believability. A video of a funnel cloud entering Central Park would give credence to rumors of a tornado in Manhattan.
Generally, credence is given to an idea or topic by something else. You'll see it often coming after words like lend, give, and impart. When something is given credence, it is made more believable. But it can also be used like this: Mary talked a lot about the poltergeist in her house. To most, her story had little credence, but I like a good ghost story, and so, decided to believe.