A notification is a message that lets someone know something has happened or needs attention. It is like a note left on your desk so you notice an update even when you are doing something else.
For example, a project tool might tell you that a teammate has shared a document. Some notifications stay visible until dismissed; others appear briefly and go away.
Use notifications for information that matters at that moment, not for every small event. Keep them understandable and give the person a way to find the related item if they want more detail.