What is an operator in mathematics? Could someone please explain the mathematical difference between an operator (not in the programming sense) and a function? Is an operator a function?
Based on your comment it sounds like you're actually asking about operations, not operators. A binary operation on a set $S$ is a special kind of function; namely, it is a function $S \times S \to S$. That is, it takes as input two elements of $S$ and returns another element of $S$. We can denote such an operation by a symbol such as $a \star b$ and then demand various additional properties of this operation, such as


associativity: $(a \star b) \star c = a \star (b \star c)$,
commutativity: $a \star b = b \star a$


and so forth. On the other hand, an arbitrary function $f : A \to B$ between two sets only takes a single input and returns an output which is not necessarily of the same type, so one can't speak of associativity or commutativity for such a thing. One might call a function $f : A \to A$ a unary operation but one still can't speak of associativity or commutativity for such a thing.
An operator is a mapping from one vector space or module to another. where a function is a map from any arbitrary set to another