What does "∈" mean? I have started seeing the "∈" symbol in math. What exactly does it mean? 
I have tried googling it but google takes the symbol out of the search.
 A: $\in$ means '(is) an element of'
For instance, 'Let $a\in A$' means 'Let $a$ be an element of $A$'
http://en.wikipedia.org/wiki/Element_(mathematics) might help you too
A: ∈ (mathematics) means that it is an element in the set of…
For eg...x ∈ ℕ denotes that x is within the set of natural numbers.
The relation "is an element of", also called set membership, is denoted by the symbol "∈". Writing
{\displaystyle x\in A} x\in A
means that "x is an element of A". Equivalent expressions are "x is a member of A", "x belongs to A", "x is in A" and "x lies in A". The expressions "A includes x" and "A contains x" are also used to mean set membership, however some authors use them to mean instead "x is a subset of A".
Another possible notation for the same relation is
{\displaystyle A\ni x,} A\ni x,
meaning "A contains x", though it is used less often.
The negation of set membership is denoted by the symbol "∉". Writing
{\displaystyle x\notin A} x\notin A
means that "x is not an element of A".
A: $\in$ means "Element of". 
For example, $a \in A$ means Element of: $a$ is in $A$.
A numeric example would be: $\color{red}3 \in \{1, 2, \color{red}3, 4, 5\}$.
