The primary flight feathers are the feathers that are normally trimmed when you clip a pet bird's wings. This keeps the bird from being able to gain height when it attempts to fly.
By Alyson Kalhagen, About.com Guide
The primary flight feathers, in many species, are the first 10 feathers on the tips of the wings.(c) 2006 Alyson Burgess licensed to About.com, Inc.