Amid widely spread concerns over social media privacy, YouTube is trying to make the difference and make users feel more comfortable by launching its "Unlisted Videos" category.
So far, the only possible way to grant people limited access to your videos was to mark those as "Private". The people you give a sesame to for viewing the video would be given an url by YouTube directly and would have to have an account. In fact, this feature only allowed you to pick 25 happy fews and you video was still listed onto YouTube's database.
Now with the "Unlisted" offer, your video remains off the board and the URL gets sent to you only - giving you the capacity to a) share it with as many people as you want and b) take full responsibility of who you give it to.
If one of your lucky friends or family members decides to post the video on a blog or social media profile such as Facebook, LinkedIn or Twitter - there goes your privacy: the video will be found and listed by search engines and visible to anyone who would like to take a look - so think before you email your mate who still thinks forwarding and 'replying all' to every email is cool...