What is pastry flour, and what is it used for?

Pastry flour is 8-9% protein so it has slightly more gluten-forming ability than cake flour.  This amount of protein will allow formation of enough gluten to hold in air or CO2 (from baking powder or baking soda).  Pastry flour is the smaller, finer particles that have been separated from flour by passing it through a sieve.  It is unbleached.  However, if doughs made with pastry flour are overkneaded, they become tough.  Pastry flour makes light, flaky products such as biscuits, pie crusts, pastries, and some types of cookies. 
 

Source(s):
OChef.com.    “What is Pastry Flour?”