Okay kiddo, so an "ardfheis" is actually an Irish word and it means a big meeting where a group of people get together to talk about important things.
In Ireland, there's a political party called Sinn Féin and they have an ardfheis every year. At the ardfheis, the members of the party come together to talk about what they want to do and how they want to make the country better.
They listen to speeches from the leaders of the party and vote on important things like choosing new leaders and making decisions about what the party should do next. It's like a big family meeting where everyone gets to have a say and make important decisions.
So that's basically what an ardfheis is, a big meeting where a group of people talk about important things.