At its most basic, Application Performance Management (APM) is the monitoring and management of the performance and availability of applications. APM is about the correlation of monitoring and management and translating that process into something that has relevance to the business application.
Essential aspects of any APM solution include what termed end-user experience monitoring (i.e. response time), end to end transaction tracking (preferably dynamic tracking), transaction profiling, baseline analysis, and reporting. IBM has an APM offering (called, guess what, IBM APM). IBM also partners with the big player in the APM space, AppDynamics.
IBM provides a component call IBM Z APM Connect. Think of Z APM Connect as a feed that sends z/OS specific information into the AppDynamics APM solution. In the following example you see references to CICS, Db2, ZCEE, VSAM etc. It's the job of Z APM Connect to send that type of z/OS specific information to AppDynamics.