An alert is a message that brings important information to someone's attention. It is like a notice on a door that tells you something needs to be seen now, such as a problem or a change.
For example, after a form is sent, an alert might say that a required answer is missing. A useful alert explains what happened and, when possible, how to fix it.
Keep the message short and put it near the thing it is about. Use urgent styling only for information that truly needs immediate attention, so people can tell important warnings from ordinary updates.