Garam masala, (Urdu: گرم مصالھ); from Urdu garam, "hot" and masala "paste", is a basic blend of ground spices to be used alone or with other seasonings. It is common in Pakistani, Bangladeshi and Indian cuisines. Usually garam masala differs according to region.
There are a variety of garam masalas you will find in India. Some common ingredients are black & white peppercorns, cloves, bay leaves, long pepper (also known as pippali), black cumin (known as shahi jeera), cumin seeds, cinnamon, black, brown & green cardamum, nutmeg, mace, and star anise, coriander seeds. Varying combinations of these and other spices are used in regional variants of garam masala.
There are many variants and each one is formulated for a specific purpose. There are numerous ways in which garam masala is prepared in different regions of India. There is no way of determining which of them are more authentic than others.