Sometimes referred to wrongly as Application Performance Management. Application Performance Monitoring is a set of hardware and/or software tools that facilitate the monitoring and management of a website or application. Basic performance monitoring might include: Monitoring the CPU of your servers. Parsing your web server access logs to see how many requests you are getting and how long they take on average. Tracking and monitoring application error rates. Monitoring network traffic to identify slowdowns. Mapping key dependencies and tracking key metrics from app dependencies like SQL, Elasticsearch, Logstash... etc.
Gartner defines application performance monitoring (APM) as one or more software and hardware components that facilitate monitoring to meet five main functional dimensions: end-user experience monitoring (EUM), runtime application architecture discovery modeling and display, user-defined transaction profiling, component deep-dive monitoring in application context, and analytics.