Chat Bubbles
From Starbounder - Starbound Wiki
Chat bubbles are a User Interface element that displays what characters type above them in a comic style word balloon. When a chat bubble is up and another appears it shows up underneath the first, creating for conversation 'threading'. Players mouths also move to coincide with the chat bubble 'speaking'.[1]
They will fade based on the distance the NPC or player speaking is from the player.