Imposter Content is when someone impersonates another person or organization and makes a false claim.
In 2019, an activist group called The Yes Men printed up 25,000 copies of a fake Washington Post newspaper and handed them out around Washington, D.C. The headline was "UNPRESIDENTED" and made the claim that Trump had stepped down from office. The real Washington Post wrote an article about it the next day.
You can read it here.
Impersonation happens so often on Twitter they had to write a policy about it. If you impersonate someone, you will be kicked off of Twitter forever.