INSTANCE_SRVTYPE is a SAP Parameter attribute which is used to control Service type of the instance 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 .
An SAP instance can provide the following services. D - Dialog B - Batch
(backgroud processing) E - Enqueue V - Update S - Spool G - Gateway M -
Message Server
See SAP Parameter Documentation for full SAP documentation for this profile parameter.