Is a set of even counting numbers well defined or not?

Yes, a set of even counting numbers is well defined. It includes numbers such as 2, 4, 6, 8, and so on, which can be expressed mathematically as the set {2n | n ∈ ℕ}, where ℕ represents the set of natural numbers. This definition clearly specifies the elements of the set, making it unambiguous and well defined.