Any
saturated hydrocarbon with seven
carbon atoms and 16
hydrogen atoms.
There are nine heptanes which comprise a set of constitutional isomers (AKA: structural isomers).
These isomers are (according to IUPAC rules): heptane, 2-methylhexane, 3-methylhexane, 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 3,3-dimethylpentane, 3-ethylpentane, and 2,2,3-trimethylbutane.