In mathematics, a set is a well-defined collection of distinct objects, considered as an object in its own right. The arrangement of the objects in the set does not matter. A set may be denoted by placing its objects between a pair of curly braces. The main property of a set in mathematics is that it is well defined. It means that given any object, it must be clear whether that object is a member (element) of the set or not. Examples include the set of all computers in the world, the set of all apples on a tree, and the set of all irrational numbers between 0 and 1. A set is a collection of elements or numbers or objects, represented within the curly brackets { }. For example: {1, 2, 3, 4} is a set of numbers.