Seamless Hyperlinks (?) [duplicate]

This question already has an answer here:

• How does GitHub change the URL without reloading a page? 2 answers

First of all, sorry for the bad terminology used here. I have no clues on what the thing I try to explain is called. Let me try:

I recently see a lot of nice websites being build with a "seamless hyperlink" system -- when hyperlinks are clicked it does not visit a url but it somehow switches to it seamlessly (no page reloading or such). Some websites do this in such a good way that it looks like the website is done as a single piece such as the flash websites of early 2000's.

I'm aware of this topic:

Here is an example to explain what I mean: http://ift.tt/Ld12VP

I'm aware of this thread: How does GitHub change the URL without reloading a page?

What I'm asking here is not pnly the "change of the url" part ut also "loading of the clicked content" part. I can modify the address bar, no problems with that. However, I have no clues on how to display different websites when a certain url is visited, or how to load a clicked hyperlink in a seamless way like the website example above.

Therefore, the question exceeds the "history api"

If my question is unclear please let me know so that I can modify it accordingly to make it more clear.

Thank you.