Verbal expression essentially means translation of mathematical terms (numbers, terms, operations, variables, ect) to words.
Say for instance; 5 + 5 = 10.
An example of a verbal expression for this mathematical equation would be five added by five results in ten.
A translation for 5(a- b) would be 5 times (5() is equivalent to 5 * ()) the difference (the result of subtraction) between two unknown numbers (variables = unspecified numbers).