| Conversation | A place where one or more users can write messages. A conversation has one or more participants, and zero or more ordered messages. |
| Guest user | A user with lightweight access to a conversation. Guest access is useful for conversations in which you don't require users to be @mentioned or to receive email or SMS notifications, for example large public group chats. Check the full overview of the differences between participants and guest users. |
| Message | An object containing text, a file (such as an image, video, PDF, or other document), or a location share sent to a conversation. A message can be either a user message or a system message. |
| Message content | The content of a message sent to a conversation, including formatting specifications. Message content can be text, files, or location shares. |
| Participant | A user who is part of a conversation. Participants can get @mentioned, receive notifications, and are listed in a conversation's participant list. |
| Role | A collection of settings with which you can customize both the appearance and features of the chat for a user or user group. |
| System message | A message sent to a conversation by the chat system or operator, instead of by a user of that conversation. |
| Session | An active connection between a user's device and your chat, as identified by your TalkJS account. A session exists from the moment a user connects to your chat, until the moment the user navigates away from the page or closes their tab. |
| User | A person or a group of people who uses your app. Each user must have a unique user ID. |
| User ID | A unique, permanent identifier of a user of your chat. |
| User message | A message sent to a conversation by a user of that conversation. |