In mathematics, particularly when dealing with fractions, the word 'of' acts as an operator that signifies multiplication. When we say 'a fraction acts as an operator of...', it implies that the fraction is used to multiply a quantity. For example, '1/2 of 10' means (1/2) × 10. The word 'of' in this context means to multiply. This concept is fundamental in understanding how fractions are applied to quantities, collections, or other numbers.