A gabfest is a time when people talk and talk — a long chat, a meeting that turns into chatter, a gathering whose main work is conversation. It is informal American English, and it usually smiles a little: nobody is calling it a grave conference. Newspapers sometimes call a political talk show or a long meeting a gabfest, as if a lot was said and not much was decided. The second half, -fest, means a lot of that thing, like a festival of talking. Though actually, fest here is the English use of a German word Fest (festival), which itself goes back to Latin festum. So gabfest is gab plus that ending, not an old English root that always meant 'meeting'. It is not the right word for a formal conference in an essay; there you would say meeting or long discussion.