Many objects in Node emit events: a net.Server emits an event each time a peer connects to it, a fs.readStream emits an event when the file is opened. All objects which emit events are instances of events.EventEmitter. You can access this module by doing: require("events"); Typically, event names are represented by a camel-cased string, however, there aren't any strict restrictions on that, as any string will be accepted. Functions can then be attached to objects, to be executed when an event is emitted. These functions are called listeners.