Alert is a word with multiple meanings depending on the context:
1. As a noun: a state of vigilance or readiness (e.g. "The police were on high alert")
2. As a verb: to warn someone of danger (e.g. "The app alerts users to new messages")
3. In computing: a pop-up notification (e.g. "The system displays an alert when the battery is low")
4. As an adjective: quick to notice and respond (e.g. "The alert guard spotted the intruder")