Notification
In a human-machine interaction system, by example a virtual assistant, a notification is a "push" message that informs the user about some relevant event, probably relevant for the user. It could be via text or voice.
The notification could be a single-turn stand-alone message, or could initiate a new conversation with user. In this case the conversation is system-initiated (see Initiative).
In a voice/voiceonly system, by example where interface devices are smartspeaker, voice notifications rise possible user experience issues. By example too much notifications are annoying and their interrupts of an active dialog have to managed with a smart dialog manager/initiative manager (see Initiative).
Majority of voice virtual assistants do not manage voice notifications and/or mixed-initiative. Amazon Alexa proposed some ProactiveEvents API[1] to manage 3rd party skills. Currently Amazon Echo Dot smartspeakers manage 1st party notification with a visual alert[2].