Player chatter encompasses lines of dialogue that are exclusive to player characters. These lines play when certain game conditions are met. Conditions that can trigger player chatter include leveling up, hitting a low health threshold, taking part in a successful combo, landing a critical hit, uncovering a new area on the map, etc. Most boons and conditions have unique associated chatter.
Combat Chatter occurs when an NPC fires off a single line in combat.
When an NPC audibly acknowledges a character upon interaction, those are its greets. Vendors in particular exhibit this behavior. It is unclear how the dialogue of the player "departing" from an NPC is categorized.
A scene is a conversation between two or more NPCs out in the world. The writing staff sub-categorizes scenes into smaller descriptors such as "ambient" and "event". An example of ambient scenes can be found in Blood Tribune Quarters, where the scene played changes depending on Rytlock's presence.
Lines of dialogue contained within a cut-scene are referred to internally as cinematic lines. Cinematics are most often used as storytelling devices for the personal story, dungeons, the living world, and trailers.