A buffer is a small amount of data that is stored for a short amount of time, typically in the computer's memory (RAM). The purpose of a buffer is to hold data right before it is used. For example, when you download an audio or video file from the Internet, it may load the first 20 percent of it into a buffer and then begin to play. While the clip plays back, the computer continually downloads the rest of the clip and stores it in the buffer. Because the clip is being played from the buffer, not directly from the Internet, there is less of a chance that the audio or video will stall or skip when there is network congestion.
Buffering (storing data in a buffer) is used in many aspects of the computer. Most hard disks use a buffer to enable more efficient access to the data on the disk. Video cards send images to a buffer before they are displayed on the screen (known as a screen buffer). As in the example above, multimedia downloaded from the Internet is commonly buffered before and while it is being played. Computer programmers use buffers to store data temporarily within the programs that run on your computer. If it weren't for buffers, computers would run a lot less efficiently. Just another thing that we take for granted.
also see - FrameBuffer