word-of-mouth: Spoken conversation from one person to another.
The hair salon’s business doubled from positive word-of-mouth from its customers.
This phrase may appear to have an unusual structure, but its meaning is quite literal: It refers to the words coming out of your mouth! “Word-of-mouth” is often used in an advertising or marketing context, in which it describes the powerful way people can spread positive or negative feelings about a brand or product through personal conversations with family or friends. It can also be used in a personal setting to generally describe spoken conversation.