Peeling is the loss of paint due to poor adhesion. Where there is a primer and top coat, or multiple coats of paint, peeling may involve some or all coats.

How to Solve
Try to identify and eliminate sources of moisture. Prepare surface by removing all loose paint with a scraper or stiff wire brush, sand rough edges, and apply appropriate primer. Repaint with a top quality acrylic latex exterior paint for best adhesion and water resistance.
This information is brought to you courtesy of the Paint Quality Institute.
-- Tips courtesy of HomeAdvisor.com