**
Domain
** -
The set of all inputs of a relation or function.

**
Function
** -
A relation in which each input has only one output. Often denoted
*f* (*x*)
.

**
Horizontal Line Test
** -
If every horizontal line you can draw passes through only 1 point,
*x*
is a
function of
*y*
. If you can draw a horizontal line that passes through 2
points,
*x*
is not a function of
*y*
.

**
Range
** -
The set of all outputs of a relation or function.

**
Relation
** -
A set of inputs and outputs, often written as ordered pairs (input, output).

**
Restricted Domain
** -
The domain of a function that is not defined for all real numbers.

**
Vertical Line Test
** -
If every vertical line you can draw goes through only 1 point,
*y*
is a function
of
*x*
. If you can draw a vertical line that goes through 2 points,
*y*
is not
a function of
*x*
.