AEM - Extend , Override , Overlay

Adobe Experience Manager (AEM) has come with many inbuilt or OOB (out of the box) components.
When we are going to design and develop a Web Page, we don't have to write the code from scratch or reinvent the wheel.
Following are the most important and very useful AEM Components.

1) Page
2) Parsys
3) iParsys
4) Carousel
5) Text
6) topnav

What is Extend?
Inheritance

1. component to component - sling:resourceSuperType

2. dialog to dialog - cqinclude, path to the parent dialog.

3. client libs - dependencies(property)
What is Override?

Create a component with same file name of the out of the box, for example, create a Page component

What is Overlay?

When a component includes a file that has the same name and relative location as a file in the component's supertype, it is called overlaying.