Word of mouth data is anything entered which was received from another person through any medium of direct communication. The origin of this data cannot be, or has not been, traced further back than the person relaying it; otherwise that further original source should be cited.

Communication of word of mouth data can be by voice, telephone, fax, letter, online chat, live video, voice message, phone text, or any other medium of direct communication between two persons (aside from email, which is categorized separately). It may be received individually or in a group (e.g. at a public presentation), or it may be overheard or relayed through a third party (in which case the first party in the chain known to the person entering the data should be cited).

This does not refer to data received in the form of published writing, videos, or other media, when the receiver is not the especially intended recipient.

Because word of mouth data is theoretically traceable to some more authoritative source or form of observation, it is generally ranked lower than most source types, especially those which can be presumed to come closer to the original observation or measurement.