-`Domain`: List of all valid **x-values** for relation, expressed as $`D = {x, x_2, x_3}`$ or as a relation such as $`D = \{x \in \mathbb{R}, x =\not 0, x <50\}`$
-`Range`: List of all valid **y-values** for relation, expressed as $`R = {y, y_2, y_3}`$ or as a relation such as $`R = \{y \in \mathbb{R}, y =\not 0, y <50\}`$