As a rule people are talking about black list feature. Android has a native auto-reject feature and we wrote about it some time ago. Whitelist is another mode when you ignore or reject all callers except selected.
There are a lot of third-party apps designed to manage incoming calls which provide blacklist and whitelist features. But most of them are not freeware and many apps are not perfect.
In this guide we will explain how to set up a whitelist on Android without any third-party apps. So, you will only receive calls and messages from those contacts that you wish. But note, other callers will be ignored but not rejected.