Announces <anything> to everyone in the same room, prepending your name. This is commonly used to express various non-verbal forms of communication. In fact, it is so commonly used that there's a special abbreviation for it: any command-line beginning with ':' is treated as an 'emote' command.
The alternate form, '::' (less commonly 'emote :'), does not insert the space between the player name and the text.
Examples:
Munchkin types this: :wishes he were much taller...
Everyone in the same room sees this:
Munchkin wishes he were much taller...
Munchkin types this:
::'s eyes are green.
Everyone in the same room sees this:
Munchkin's eyes are green.