A "signifier" is a term used in linguistics and semiotics to refer to the physical form of a sign. This can be a word, image, sound, or gesture that conveys meaning. For example, the word "tree" is a signifier that represents the concept of a tree, which is a living organism with a trunk and branches. In communication, signifiers help us understand and interpret messages. They are essential in conveying ideas and emotions. For instance, a smile can be a signifier of happiness, while a frown may signify sadness. Understanding signifiers allows us to decode the meanings behind various forms of expression.