There is a new privacy level of distributing videos in YouTube. Previously you have a choice of inviting a maximum of 25 people who could see the video or public distribution.
There is now the option of setting the video privacy level to unlisted.
This means that the video will not appear in the public streams or on your YouTube channel. Only the people you send the link to will be able to see the video.
This is good news/bad news kind of deal. The good news is that you are no longer limited to 25 people. If there is a group of folks that you want to view the video this is a good thing.
The bad news is that if you have a stinker in the group and if they post the link then other people will be able to access the video. This does not bode well for teenage girls of shifting alliances.
In other words, you do have to know and trust the person.