About Lesson
Set is the collection of well-defined objects. By definition, it means that anyone should be able to tell whether the object belongs to a particular collection or not.
The objects in a set are referred to as the elements of the set. A set can have finite or infinite elements.
For example: A = {3,6,9,12,15,…} are the elements or members of a set
Note — (the three dots) means infinity