In HTML you cannot embed one HTML page within another HTML page, In PHP, there is include or require statement for it. Which you has to add on the section following with file name where you want to insert the content.
Where can I use it ?
Using embedding, you can reuse the same code within another page and it saves our time. For example, you are creating a project which contains the number of pages, all pages need the common header and footer. So, you have to write header and footer code on all pages and later in future, you need to add one more menu item in the header so, you go to all pages and add a new item to it.
For solving these types of problem you can create the separate file of it and include in your where it required.
AngularJS allow us to embed HTML page within another HTML page using ng-include directive.