What is Application Performance Management?

Legal Definition
In the fields of information technology and systems management, application performance management  (APM)  is the monitoring and management of performance and availability of software applications. APM strives to detect and diagnose complex application performance problems to maintain an expected level of service. APM is "the translation of IT metrics into business meaning ([i.e.] value)."
-- Wikipedia
Legal Definition
The testing and monitoring of a companies computers and their software. It is used to fix problems and manage performance.