enque/replication_dll is a SAP Parameter attribute which is used to control Name of the shared library for the enqueue replication information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
Full path name of the shared library or DLL of the platform-dependent
enqueue replication subsystem (if available). This parameter is only
relevant on the enqueue instance.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.