Whether buffering is a sort of downloading?

Question

buffering = downloading

Answer 1

It's more like

buffering = downloading to cache

After done, and after you closed the browser, it all gone - that YouTube video, that MP3 stream, that login information.

Answer 2

buffering = downloading to a temporary storage

when you are watching online videos and you don't have fast enough connection, you may see the word "buffering" in your player, that means that your player is downloading the data to a temp. storage then start to display it to avoid cutting video.