Twitter has created a new help center page that explains everything about the Twitter Circle. It’s not the same as Twitter Communities, and it’s not the same as having a secure account (where tweets can only be seen by those with permission).

Twitter Circle can be described as the equivalent of a “Close Friends” list on social media. When you tweet to your Circle, only those added to it will be able to see and reply to your tweets.

Currently, you can only have one circle, and the number of people in it is limited to 150 users. Only you can see the full list of users in your circle, and tweets posted in your circle cannot be retweeted. While Circle restricts who can view certain Tweets, it doesn’t stop them from re-sharing media or screenshots of your content. Finally, once you have been added to a Circle, you cannot remove yourself from it.

Twitter is only testing this feature for some users around the world. To find out if you’re part of the test group, you should see the option to create a “Circle” popup when tweeting on Android, iOS, or Twitter.com.

Anyone can become a part of the Circle, even those you don’t follow. Only members of your Circle can see, reply to, and read replies to your Tweets when they are posted in your Circle.

We’ve already reported that Twitter started testing Twitter Circle today.