Basically, Twitter Circle is Instagram’s Close Friends or Facebook’s “select audience” feature. It’s a way to filter who sees specific content that you post, without having to lock-down your entire account. With Circle, for every tweet you post, you’ll have the option of sending it out to everyone or a smaller group.

Twitter Circle allows users to pick up to 150 people (followers or not), as a select audience for some tweets. When you send out a tweet directed to your Circle, only those chosen few can view and interact with the original tweet and its replies. Members of your Circle can’t see a full list of everyone else in the same Circle (only you, as the Circle’s creator, can do that), and members also cannot retweet what is posted beyond your Circle.

For now, users testing the feature can only create one Circle— meaning that you can’t readily shift your specialized audience from tweet to tweet. Further, you can’t remove yourself from another person’s Circle, but you can mute a thread like normal.

In the FAQs, Twitter specified that the Circle feature is different from Twitter Communities, which the company introduced last year and also narrows tweet audiences by mimicking Facebook groups and Reddit threads. Twitter Communities can be made up of anyone on the site invited to participate in a specific discussion, while Circle is “for sharing the Tweets you only want to share with the people you chose to see them.”

Twitter Circle is currently only available to a limited number of people in the test group through iOS, Android, and twitter.com. You’ll know if the feature is available to you if you see a prompt to create a Circle when you go to post.