em/use_emode_mapping is a SAP Parameter attribute which is used to control if set to true, the emode mapping (emode window) is used 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 .
Specifies whether emode mapping ("emode window") is used.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.