谈谈 (tán tán) is the reduplicated form of 谈 (tán, to talk or discuss). Verb reduplication in Mandarin adds a sense of doing something briefly, casually, or tentatively - so 谈谈 means to have a quick chat or talk a little about something. It softens the request compared to 谈 alone and is common in conversational invitations such as 来谈谈 (let's talk) or 想谈谈 (want to discuss).