What is Monitoring?
Monitoring is the act of collecting, aggregating and analyzing information to understand how an application is doing.
Monitoring is the act of collecting, aggregating and analyzing metrics to understand how a system works. If you ever took a ECG using a smart watch, you monitored during few minutes your heat beat rate.
Monitoring is essential to cloud applications and people managing them, in order to know if an application or services are working as expected (diagnostic monitoring). They use it to improve their understanding of their app and react in case of emergencies.