Every chat is a conversation but not every conversation is a chat. Chats are typically short. But not always. The main semantic feature of a chat is informality. Generally, an unscheduled conversation between two people. A secondary feature can be shortness and off-the-cuffness.
That said, AmE tends to go with conversation and BrE tends to go with chat.(Unlike the question recently posed here about have/have got). But the word chat is also used in AmE. Also, in AmE, talk is used instead of chat. "I ran into my neighbor in the street, and we had a talk about that." versus: "I ran into my neighbour in the road, and we had a chat about that".
These comments do not apply to the use of word chat on the internet but apply to what goes on in the real world.
Meetings typically (business and that type of meeting) involve a discussion among participants but typically do involve conversations. Conversations are typically between two people, though one can say, for example, a three-way conversation. When you attend a meeting, there can be a number of participants, and what is discussed (when not voting etc.) can be called a discussion. Each person presents her/his views or responds to others' views or opinions.
Typically, meetings do not involve "conversations" except in the now current usage of the word among journalists and talking heads who call everything a "conversation" and a "narrative". So, I can imagine a journalist referring to say, a meeting at the White House among 10 people, and when reporting on it, calling it a ""conversation". But technically, discussions at meetings are not called conversations.
Conversations and chats can be long or short. ((We had a long/short conversation about x, We had a long/short chat about x). Also, conversations and chats can also be discussions. They become discussions, one might say, if they involve a serious topic that is gone into at length by the two people having them.