Chats cover 1-on-1 Chats as well as private group Chats.  When you create a Chat, it will automatically be set to Private, regardless of the number of members invited.  Private Chats will always be available in the "Private" tab of "My Chats" irrespective of the amount of activity that takes place in the Chat.

Parties cover group Chats that are public and joinable by any non-blocked users.  Any users may search for active Parties using the "Live Parties" section on the homepage. ("Discover"). Parties are then either online or offline but Parties in both modes will show up in the "Parties" tab of "My Chats."

Group Private Chats and Parties share many features and you may find functional similarities in both.  For example, the Admin Portal in both contain many similar options and functions, so please be sure to check help articles for both Private Chats and Parties if you cannot find the help you are looking for.