| domain | the set of all possible inputs of a function which allow the function to work |
| excluded value | a value for a variable that is not allowed in an expression, such as a variable in a rational expression that would make the denominator equal zero |
| extraneous solution | a solution that results from solving an equation that is not a valid solution in the original equation |
| rational equation | an equation that contains one or more rational expressions |
| rational expression | a fraction with a polynomial in the numerator and/or denominator |