PGT stands for Post Graduate Teacher — a teacher holding a master's degree along with a teaching qualification, who typically takes the senior-secondary grades, Classes 11 and 12. It is the most senior of the common teaching grades, above TGT and PRT. The distinction is about the level taught and the qualification held, not a separate kind of contract.
In Indian schools
A PGT is one more staff role on the rolls, tied to the senior batches and subjects they teach. A school management system's job around staff is to hold the record and control access by role, which RaivatEdu does at the database level.