What does "idle" mean on Facebook?

Being idle on Facebook is the same concept as on other instant messaging clients, such as Skype, AOL and MSN. When a user has not been active on a particular platform, meaning that he has not clicked around the program or messaged anyone, it means that he is idle.

Opposing Views states that Facebook previously displayed a half-moon symbol to represent an idle user. Since 2011, the social networking site uses green dots to represent users who are active. For those who are idle, Facebook displays a numerical figure with an "m" for minutes or "h" for hours next to a mobile phone icon. This means the user has not been active in that amount of time.