What is real time streaming?
Think of real time streaming as being broadcasting for the internet. Real time streaming requires specialist server software to broadcast content (usually video and radio) over the internet. It works just like your TV or radio. If your connection isn't fast enough or the network becomes congested, then playback may glitch or mute. When it resumes you will have missed a bit.
You cannot usually rewind or review a real time stream because it usually does not cache or buffer.
What is HTTP streaming?
HTTP streaming is not really streaming at all but a clever way to make playback begin before a file has completed downloading. As long as the data rate of the connection is greater than the data rate of the audio or video file being "streamed" (downloaded really), it will seem to play in real time.
HTTP streamed files are usually cached in RAM (QuickTime does but Windows Media doesn't seem to) and so can be saved to disk and played again.