Formal:
* Conversation: A general term for a spoken exchange of ideas.
* Dialogue: A formal, extended exchange of ideas, often used in literature or philosophy.
* Discourse: A long and formal discussion on a particular topic.
* Conferment: A formal meeting or discussion.
Informal:
* Gabfest: A lively and informal chat, often about nothing in particular.
* Yarn: A long and rambling story or anecdote.
* Chinwag: A casual and friendly chat.
* Shoot the breeze: To talk casually and informally.
* Catch up: To talk about what has been happening in each other's lives.
* Hang out: To spend time together casually, often involving talking.
* Rumination: To think deeply and at length about something.
Other options:
* Discussion: A more serious and focused conversation.
* Debate: A formal and often heated discussion on a particular topic.
* Rhapsody: A long and enthusiastic speech or conversation.
* Harangue: A long and angry speech.
The best word to use will depend on the specific situation. For example, if you are talking about a casual chat with a friend, "gabfest" or "chinwag" might be appropriate. If you are talking about a formal discussion on a serious topic, "discourse" or "dialogue" might be a better choice.