The fallacy of four terms, also known as quaternio terminorum, is a formal fallacy that is committed in a categorical syllogism that has four terms. A logical fallacy is an error in logical argument which is independent of the truth of the premises. ... In traditional logic, a syllogism is an inference in which one proposition (the conclusion) follows of necessity from two others (known as premises). ...

Example:

All humans are alive, animals are mammals, therefore all humans are mammals.