$\displaystyle

\bigcap S

$ denotes the set $\displaystyle

\left\{ {x;\

\forall X

\in S,x \in X} \right\}

$

for any non-empty set S

And $\displaystyle

\bigcup S

$

denotes the set $\displaystyle

\left\{ {x;\

\exists X

\in S,x \in X} \right\}

$

for any set S

Does anyone know how to explain waht it's mean?

Can it be explain using Venn Daigaram?