Maida flour is a very finely milled flour used in Indian cooking for making pastries, breads, and various biscuits and in particular parotta. Maida is milled from the wheat endosperm only so it is quite refined and very starchy. While the flour is typically made from wheat but it is made from tapioca in some parts of India.
This is easy to find in most any Indian grocery store. You can also purchase it online at Amazon.com: Rani Maida Flour.
If you don't have maida flour then you can substitute one of these alternatives:
Is maida flour the same as "plain flour"? Plain flour is the British term for all-purpose flour, so the answer is no, it is not the same. Although maida flour is sometimes referred to as all-purpose flour in India, it is not the same thing as U.S. all-purpose flour.