The new access level is called "unlisted", which means that only people who know the address of the video can view it. "The video will not appear in any of YouTube's public spaces, such as search results, your channel, or the Browse page, but the link can be shared with anyone."
To watch an unlisted video, you don't need a YouTube account and there's no limit for the number of people that can watch your videos. Anyone can link to the video, but it won't be indexed by search engines.
"Even though your video will not appear in any of YouTube's public spaces, links to the video could still appear elsewhere on the web if anyone who knows the video's URL shares it. It is therefore up to you to maintain the privacy of your video and the unlisted URL. You can further restrict the video at any time by returning to your account and marking the video as Private," explains YouTube's help center.
{ via YouTube Blog }