The term buffering is not uncommon to the internet and is especially associated with video downloads. In buffering, the computer basically uses a temporary physical storage area that holds the date while the CPU manipulates it and then transfers it from one device to another. Since it is a temporary storage unit that holds the data for a limited time only, if not saved then the data can be lost.
When you see online videos and don’t want to download it then also buffering is used. The video streams on your computer so that you can see it without downloading the video. When you click on the play button then the computer takes a little before starting the video. During that period it buffers the video and stores in a temporary place and then shows you the output only when the video has streamed well enough to be viewed. The buffering time depends upon the internet traffic and a longer time would make your video a little slow and static. The buffering time is also dependent upon the player that you use for viewing the video. If the internet connection and the player used are not efficient then buffering takes a lot of time and the user may feel annoyed with it.