well-defined sets
A well defined-set means the element is a member of the set or not.
Example
A = {1,3,5,7}
This set is consist of the first four odd numbers. That is a well-defined set.
X = {Biryani, Custered}
This set is consist of two distinct dishes. This is a well-defined set.
Not well-Defined
If the element of a set is not well defined then it is called undefined set.
