Can't find airplay icon on my iPhone iPad iPod MacBook

Cant find airplay icon.Why I can't see airplay option , where is airplay , what is airplay, how to download airplay, how to install airplay.iPhone 5s iPhone 5 iPhone 5C iPhone 4S iPhone 4 iPhone 3GS ipad retina display ipad mini ipad 1 ipad 2 ipad 3 ipad 4 ipad retina mini iPod touch . iOS 7, iOS 6 iOS 5 iOS 4 iOS 8 Why don't I see airplay option Airplay icon missing