A set is a well-defined collection of objects may be defined items or entities sharing some common property .
Each object in a set is called a member or an element of the set ,and elements in a set do not repeat
DESCRIBING SETS
There are two common ways for defining a set:
1 By roster or listing the elements of the set.
The elements of a set are often listed by roster.
A roster is a list of the elements in a set, separated by commas.
The elements of a set are written inside { }