abap/heap_area_dia is a SAP Parameter attribute which is used to control Limit of heap memory per dialog work process 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 the maximum local process memory (heap, malloc) that can be
allocated to a single dialog work process. The aim is to limit the size
of a user context if required.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.