With or without you realize, your everyday code is using one or many design patterns which are going to be introduced in this post. If you google for Design Patterns, there will be a bunch of blog posts, books that talk about this topic. The recommended book is the canonical

It is often to design a system where the owner does not want to reveal all their data to anyone or be anonymous. For example, bloggers want anonymous users to be able to view their blog posts but they never want any other than editors to be able to edit