Multiplayer is a mode in Wesnoth where you and hundreds of other players can battle in matches. You can chat or battle in this mode. You can also battle locally.
When you create a game, other people can join. You can decide how much gold every player gets. If you join a match, you can choose a race.
You can play with AI or with other people in the same room as you, on the same computer.
You can chat during online matches, or when your in the lobbey. The chat is not monitored.