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