Masala is a blend of ground spices. In Indian cooking, it is widely used for flavouring dishes. Some specific blends or combinations are very popular such as Garam Masala, Tandoori Masala, Chat Masala, Biryani Masala, etc.
All these Masalas have some spices in common and by adding other ones they provide specific flavours to each Masala. There are also different versions of Masalas depending on the region.
There are varieties of Masalas are available in the market, but I always prefer to make them at home.