Given two [[Set|sets]] $A$ and $B$, one can form a set from them that consists of all the elements of $A$ together with all the elements of $B$. In other words, it is the set of all elements from $A$ or $B$ (or both). This set is called the union of $A$ and $B$ and is denoted by $A \cup B$. $A \cup B=\{x \mid x \in A \ \lor\ x \in B\}$