Apple App Store Principles and Practices

We created the App Store Review Guidelines to provide clear guidance to developers on building the best apps for our customers. The five pillars of the guidelines — Safety, Performance, Business, Design, and Legal — require that apps offered on the App Store are safe, provide a good user experience, adhere to our rules on user privacy, secure devices from malware and threats, and use approved business models. And the App Review team makes about 1,000 calls a week to developers to help them diagnose and resolve any issues that led to rejection — so they can get their app onto the App Store.

Source: www.apple.com