Monitoring means regularly watching an app to see whether it is healthy and responding as expected. It is like checking a few dashboard lights while a car is running.
A team may watch whether a website is reachable, how long pages take to load, or whether errors are increasing. If something unusual happens, an alert can help someone investigate sooner.
Monitoring does not prevent every problem by itself. It helps people notice changes, but the team still needs to understand the alert and decide what to do.