Sets - Definition
Simply a set is a well-defined collection of objects. The collection could be of anything.
For example
Collection of all of states in India
Collection of vowels in English alphabets.
Collection of total countries in world.
Collection of all living organisms
Collection of all plants.
All of the above discussed are examples of Sets.
The world well-defined is very important. The objects stated in the collection should belong to the set. There should be no confusion or ambiguity for the object to be the part of the set.
For example defining a set as: Collection of the five most beautiful flowers. Now, the word "most beautiful" is not very much well defined. For someone most beautiful flower could be rose, for other person it could be lily. So this is not very much well defined, therefore is not a set.