Downloading the first block of data. In streaming media, buffering refers to bringing in an extra amount of data (filling the buffer) before playing the audio or video. Having more audio data or video frames in memory than are actually needed at each precise moment compensates for momentary delays in transmission from the source.

When a network is fast enough to keep up with playback, buffering is not necessary; however, this is not the case over the Internet where packets can traverse a dozen or more routers from source to destination, and delays can be introduced at any juncture. See streaming video, buffer and buffer flush.