A set is collection of well defined objects.A set can be written explicitly by listing its elements using set bracket.
Every object in a set is unique: The same object cannot be included in the set more than once.
For example, India is a collection, or set, of 29 states plus.
The 29 individual states are the members or elements of the set that is called India.
WELL-DEFINED SET:
A set is well-defined if there is no ambiguity as to whether or not an object belongs to it, i.e., a set is defined so that we can always tell what is and what is not a member of the set.
Example: C = {red, blue, yellow, green, purple} is well-defined since it is clear what is in the set.
Example:‘The rivers of lndia’ is a Well—defined collection. Since, We can say that the river Nile does not belong to this collection. On the other hand, the river Ganga does belong to this collection.
In the above diagram we can say which planets are present in solar system.So it is example of well defined set.
Differences between well defined and not well defined set