If the management course is being offered by an autonomous institute, meaning it is not affiliated to any university it cannot offer a Degree in managment and hence it offers a Post Graduate Diploma in Management. At the end of the course you are offered a Diploma in Managment.

And if the same course if offered by a University it is called a Masters in Business Administration. At the end of the course you are offered a degree in Managment.

Both MBA and PGDM are equal in value if done from one of the good colleges or institutes.