What is the blue triangle of apple?

This icon refers to the AppStore.

There is a blue triangle in the AppStore icon, which represents various applications in the AppStore. The design of this icon is simple and clear, and people can recognize it as an Apple product at a glance.

AppStore is a digital mobile application publishing platform created and maintained by Apple for iPhone, iPodTouch and other products, which allows users to browse and download some applications developed by iOSSDK or MacSDK from the AppStore.