The act of expressing, conveying, or representing in words, art, music, or movement; a manifestation: an expression of rural values. Something that expresses or communicates: Let this plaque serve as an expression of our esteem. Mathematics A symbol or combination of symbols that represents a quantity or a relationship between quantities. The manner in which one expresses oneself, especially in speaking, depicting, or performing. A particular word or phrase:"an old Yankee expression .. 'Stand up and be counted'"(Charles Kuralt). The outward manifestation of a mood or a disposition: My tears are an expression of my grief. A facial aspect or a look that conveys a special feeling: an expression of scorn. The act of pressing or squeezing out. Genetics The act or process of expressing a gene.