The meaning of equivalence classes from Myhill Nerode Theorem is the no of states in the minimal dfa.
Given:Number of equivalence classes w.r.t language,
L={(a^n)(b^n)(c^n)| n>=0} is
First of all the dfa will contain infinite states because no dfa is possible as it is not a regular language .. what they mean possibly is that they will have states for all possible values of n ranging fromm 0 to infinity and thus the dfa will contain infinite states.