How do I archive a conversation? What’s the difference between archiving and deleting?
Archiving a conversation hides it from your inbox until the next time you chat with that person, while deleting a conversation permanently removes the message history from your inbox.
To archive a conversation, go to your main messages page and click the x next to the conversation you want to archive.
Once you do this, the conversation's history will be preserved, and you'll still be able to find it later. If the same person sends you a new message, the archived conversation will reappear in your inbox, and the new message will be added to it.
Learn how to delete messages.