Besan is a flour made from a variety of chickpeas grown in Southern Asia. In India this variety is called Desi Chana which is roasted and then milled into flour called Besan.
Note: Regular chickpea flour is similar to but not the same as Besan.
Besan is also called Palari or Chana powder. In Indian cooking Desi Chana and Kabuli Chana are the two varieties of chickpeas used to make Besan. Desi Chana is smaller than Kabuli Chana, yellowish in colour and more popularly used to mske Besan. It is lightly roasted before milling into various grades of coarseness from very fine like Maida (all-purpose flour) to gritty like Sooji (Farina). Professional cooks in India may use up to five different grades of coarseness of Besan. Fine (or Superfine) is the most common grade used at home (as an Atta to make Missy Rob or Cheela) but you may need a grittier grade to make Laddoo or Halwa.