It's not about CEM, just Introscope.
Entry Point detection is part of Smart Instrumentation which was first introduced in 9.7.
The docops glossary has a useful definition:
Glossary - CA Application Performance Management - 10.5 - CA Technologies Documentation
When smart instrumentation and automatic entry point detection are enabled, Introscope automatically monitors threads that are involved in client socket call transactions. Entry points are the transaction beginning points. Entry points display in the agent-centric tree and transaction traces.
See also: smart instrumentation, automatic backend
See also this video
January 2016 - APM Community Webcast - Smart Instrumentation and Entry Point Detection
Hope that information helps. Please let us know if you have additional questions.
Many thanks Lynn!!