Operation

An operation is a function which takes a predefined finite number of inputs and whos domain is a power of its codomain.

For example: if given a set $S$, an operation could look like this: $S\times S\to S$ Since it takes two inputs, it is a binary operation.

The number of inputs an operation takes is called its arity

nullary = 0 inputs unary = 1 input binary = 2 inputs ternary = 3 inputs 4-ary = 4 inputs …

Terms

In an algebra a term is a function defined by composing its operations. example of a term in a ring with the operations + and *: $(a+b)\cdot c$