Lifestreaming, as you probably know, is all about sharing your daily activities (both in the online and offline world) with friends and family. (See how to create a Lifestream with Google Reader).
You upload a picture on the web, you change your current geographic location on the phone, you favorite videos on YouTube, you comment on a friend’s picture, you change your status in messenger.. all these events are captured and show up in your "lifestream" in reverse chronological order.
Sounds simple but in case you need help in explaining the whole concept of lifestreaming to someone who is very new, show them the video above.
Microsoft will soon be adding lifestreaming capabilities into Windows Live and they recently hired the Common Craft guys to do a video that helps explain the whole concept in plain English. The video obviously talks only about Windows Live products but the concepts can easily be applied outside Live as well.