A notification is a message or alert delivered to a user to inform them of important events, updates, or actions that require their attention. Notifications can appear in various forms, such as pop-up messages, banners, emails, or push alerts on devices. They are commonly used in applications and websites to keep users engaged, provide timely information, or prompt specific actions, such as confirming a transaction or responding to a message. Effective notifications are clear, concise, and relevant to the user's needs.