This is an object definition, the main chunk for an object and the first loaded by the VM. There can be multiple master OBJDs in an IFF, meaning that one IFF file can define multiple objects.
The ID of the BHAV that contains the code making up the main function for this object. A value of less than 4096 refers to a global subroutine, less than 8192 means local, anything above that means semi-global.