Guid is defined for SMM variable module to notify SMM variable wrapper module when variable write service was ready.
Include/Guid/SmmVariableCommon.h

GUID Information

GUID's Guid Name	GUID's Guid
gSmmVariableWriteGuid	{ 0x93ba1826, 0xdffb, 0x45dd, { 0x82, 0xa7, 0xe7, 0xdc, 0xaa, 0x3b, 0xbd, 0xf3 }}

Refer to Header File