Word of mouth, is a reference to the passing of information by verbal means, especially recommendations, but also general information, in an informal, person-to-person manner. Word of mouth is typically considered a face-to-face spoken communication, although phone conversations, text messages sent via SMS and web dialogue, such as online profile pages, blog posts, message board threads, instant messages and emails are often now included in the definition of word of mouth. There is some overlap in meaning between word of mouth and the following: rumour, gossip, innuendo, and hearsay; however word of mouth is more commonly used to describe positive information being spread rather than negative, although this is not always the case.

http://en.wikipedia.org/wiki/Word_of_mouth