@_chris A notification is to inform the user of something that has happened, because of user interaction or a third party service that called a webhook (e.g. payment service that informs your app a payment has been received). An announcement is to inform a user or group of users of something that is going to happen. This is outside of the users' control.
Code wise, there isn't any or not much, difference I believe. It's just semantics and split for the users' convenience.