This is a red spicy powder made up by grinding dried chillies. There are many different grades of red chilli powder from a Kashmiri chilli powder which is a mild chilli but gives a vibrant red colouring to dishes right through to a Birds eye chilli powder which gives a much more fiery heat.
Red chili powder is finely ground from sun dried chili peppers, most often a blend of very hot, small chilis. This can be thai red chilis, Indian guntur, byadgi, or gunthur. This powder is to be used sparingly, in pinches, and the primary purpose of red chili powder in Indian cooking is to add spice to Indian dishes.
Red chillies are hollow, and the pith and seeds are the hottest part. Many red chillies are milder than green chillies, although there are hundreds of varieties. Chilli heat is related to capsaicin content and measured in Scoville units.