Monitor means to watch, observe, or check something carefully over time to see how it's changing or to make sure it's working properly. A teacher might monitor students during a test, walking around the classroom to ensure everyone follows the rules. Doctors monitor patients' vital signs, like heart rate and temperature, to track their health. Scientists monitor the weather, recording patterns and changes to predict storms.

The word suggests steady, ongoing attention rather than a quick glance. When you monitor your progress on a long-term project, you regularly check how you're doing and adjust if needed. The person doing the monitoring is called a monitor: many classrooms have student monitors who help keep track of supplies or assist with daily tasks.

A monitor is also the screen you look at when using a computer. This type of monitor displays information so you can see what the computer is doing. The name makes sense because you use it to watch and track your work.