Relier Pairs Lesson 20 VocabularyVersion en ligne Match the term and definition with the example. par Tracy Harrison 1 Equivalent Expressions: Two or more expressions in different forms that always name the same value. 2 Variable: A letter that represents an unknown number. In some cases, a variable may represent more than one number. 3 Solution of an Equation: A value that can be substituted for a variable to make an equation true. 4 Substitute: To replace one thing with another.