Like affirming the consequent is a logical fallacy in the form of modus ponens, denying the antecedent is a fallacy in the form of modus tollens. Recall that modus tollens uses the premises
P = > Q
to conclude ~P.
Denying the antecedent uses the premises
P => Q
to conclude ~P. However, this is not a valid argument; P may or may not be true based on the information presented.
Denying the antecedent gets its name because one of the premises denies (negates) the antecedent of the implication.