Something that you heard from other people you know by word of mouth. Example: "How did you hear about this party?" Reply: "Word of mouth."

When you say that you heard something word of mouth, you are not being specific about whose mouth you heard it from; just that you heard it from another person. Example: "There has been talk at school about canceling the concert." Reply: "Really? Who did you hear that from?" Answer: "Just word of mouth."

We do rely on what other people tell us, so word of mouth is one important way that we learn things. If something is "only" (or "just") word of mouth then you might not know where the "word" really started or how it changed as it went from "mouth" to "mouth". Example: "Did you hear they finally arrested that guy?" Reply: "Yes, but that's only word of mouth." Example: "Where did you hear that?" Reply: "Just word of mouth."