The intersection symbol takes the shape of a horseshoe opening downwards. The intersection is used in math to indicate that if you have two sets of elements, the intersection is the group that incorporates the common elements, creating a new set of elements.
The intersection is considered to be an associative operation since any set of a, b and c, a ∩ (b∩c) = (a∩c) ∩ c. The intersection is commutative, for example in a and b a ∩ b = b ∩ a. If you have a group of sets a,b,c and d; it can be written like this: a ∩ b ∩ c ∩ d.