"Crank" is a slang term for someone infected with the Flare virus. "The Gone" is another term used for a stage of viral progression in those infected, when a person is past humanity and has lost what sanity they had.
In the film series, Cranks are depicted as zombie-like creatures with strange vine-like growths protruding from their bodies. The book series clearly defines differences between Cranks and regular zombies, however, as Cranks remain alive and somewhat can speak. They both, however, are described as cannibalistic humanoids.