The full form of "hmm" in chat is not a standardized acronym or abbreviation. According to, "hmm" is usually used in chats and doesnt have a definition. It generally means that the person is thinking about something you said or asked. Sometimes, it can mean that the person totally agrees with your message and its a kind of "yes". However, some people use "hmm" as a hint to tell the other person that they are not interested in the conversation, so lets finish. If two or more consecutive messages only have "hmm", that means that the person is bored, sleepy, and eagerly waiting for you to say goodbye. It is not necessary that if someone types "hmm", that person definitely does not want to chat, it may be their nature. Maybe that person has a habit of saying "hmm" while agreeing or something. So its better to understand the situation and then come to a conclusion.