Copper sulfide CuxS (x = 1–2) is a non-stoichiometric compound. This kind of compound can be formed because copper can have +1 and +2 oxidation states. The compounds Cu1.75S, Cu1.8S and Cu1.97S contain both Cu+ and Cu2+ in their structures.
They also refer to the defects in the compounds; actually what Mr Wattanathana said already it is another interpretation for the above non-integer values of "x".