abap/heap_area_total is a SAP Parameter attribute which is used to control limit of heap on Appl.Server 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
specified in total by all work processes. The aim is to avoid a swap
space bottleneck if user contexts become too large.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.