What Does "Friends Online" Mean on Facebook?by Lee Tea
Besides being an excellent place to read and share status updates, links and photos, Facebook also makes a great place to connect with friends via instant messages. While you can send messages to your Facebook friends at any time, Facebook's chat feature enables you to send and receive messages in real time with friends who are currently online.
Facebook's real-time chat feature is located on the bottom right portion of the screen. When you're signed in to Facebook, a list of your Facebook friends who are currently online is displayed in a white box beneath your updates ticker. Currently online friends are indicated by a green dot next to their names. Over time, Facebook compiles a list of friends you chat with frequently at the top of that list, and these friends show up on the list regardless of whether they are online or not. To check if they are online, look for the green dot next to their names. If they aren't currently online, you can still send them a message, but they won't get it until the next time they sign on.
Managing Facebook Chat
When you are online, a green dot appears next to your name when your friends look at their list of who is currently online. To visit Facebook without making yourself available to chat, click the gear-shaped logo beneath the list of online friends in the bottom right corner of the screen and select "Turn Off Chat." You can also use the options in "Advanced Settings" to permanently appear offline to certain friends of your choosing. This can be helpful if you receive many unwanted instant messages when you visit Facebook.