The sample space S of an experiment is the set of all possible outcomes of the experiment. An event A is a subset of the sample space S, and we say that occurred if the actual outcome is in A.
The union of two sets, denoted by $A \cup B$, is a set containing all elements between all elements in set A or in B.
For example, $\{{1,2}\}\cup\{2,3\} = \{1,2,3\}$.
The shaded area shows set A∪B, which is equivalent to B∪A.
The intersection of two sets, $A\cap B$, is a set containing all elements that are both in A and in B. Typically, $A\cap B \le A\cup B$.
For example, $\{{1,2}\}\cap\{2,3\} = \{2\}$.
