'push' notification, This is a notification that comes up on your device that doesn't seem to be 'attached' to anything! It's not a text or other message, and not on a website, but it is a message that comes from either an app or a website where you have at some point selected (deliberately or not) to allow such 'push' notifications. These are usually either News or Security/Safety related notifications, but can also simply be notifying you of new products etc., and are deliberately designed to get your immediate attention. They can also be scams pretending to be a security notice or bargain offer!
If you want to stop these, de-select them on your web browser, or on the associated app..