A **reminder** is a prompt or notification designed to help someone remember an event, task, or piece of information at a specific time or under certain conditions. Reminders can be created and delivered through various means, such as:

1. **Personal Reminders**:
   - Writing notes or to-do lists.
   - Setting an alarm or alert on a device.
   - Using a calendar to schedule tasks or appointments.

2. **Digital Reminders**:
   - Notifications from apps like calendars, task managers, or reminder apps (e.g., Google Calendar, Microsoft To-Do).
   - Email or SMS reminders sent automatically.
   - Smart assistants like Alexa, Siri, or Google Assistant providing alerts.

3. **Visual or Physical Reminders**:
   - Post-it notes placed in strategic locations.
   - Objects intentionally placed to trigger memory (e.g., a packed bag by the door to remember to take it).

Reminders are particularly useful for time-sensitive tasks, important dates, or routine activities and can be customized to fit personal needs and schedules.