Let $V =\{a, e, i, o, u\}$ and $B =\{a, i, k, u\} .$ Find $V - B$ and $B - V$

We have, $V - B =\{e, o\},$ since the elements $e, o$ belong to $V$ but not to $B$ and $B - V =\{k\},$ since the element $k$ belongs to $B$ but not to $V$

We note that $V - B \neq B$ - $V$. Using the setbuilder notation, we can rewrite the definition of difference as

$A - B = \{ x:x \in A$ and $x \notin B\} $

The difference of two sets $A$ and $B$ can be represented by Venn diagram as shown in (Fig) 

The shaded portion represents the difference of the two sets $A$ and $B$