IPhone- what is photo stream

I just upgraded to an iPhone 4 and iOS 5.1.1

Now there's a "photo stream" album in my photos app. Wtf is this? I'm extremely protective of my iPhone and the information on it. What is this photo stream? What does it do?
I don't want any photos to be accessible anywhere or anyhow except in the iPhone

Photo stream does not send strangers your pictures! Photo stream does however send your photos to all your iOS devices.
So say you have a iPhone and an iPad. It would send photos taken from your iPhone onto your iPad. And photos taken from the iPad to the iPhone. It doesn't send them to strangers, but it easier for others to hack your device and see the photos send between your iOS devices. So I always have mine off just in case!

  • Why do I have photo stream on my iPhone? I realized others with the same IPhone I have have 'Places' instead of 'Photo Stream.' Why is this? I want to get rid of Photo Stream if possible and just use my Camera Roll.
  • What's photo stream on iPhone 5? I got an iPhone 5 yesterday and my sister has a 4 and some how on whatever photostream is it gave me her photo like I have no idea how? Does anyone know?
  • What is photo stream on the iPhone? Hi so I just recently got an iphone! I went for a few weeks without using iCloud but then I recently decided to get it. I noticed under my pictures that there's a new tab with "photo stream" and only the pictures that I took after I used icloud? What is that? Does that mean only my pictures that I took after I got iCloud will be on iCloud?
  • What does turning off photo stream on iPhone do? If I turn it off will it still put my pictures in photo stream and other people can see them? Or will it just like not put my pictures in photo stream anymore for people to see?