it means that that person is not online.....
that person is logged in but may be away from their computer on doing something else other than gmail.
On Gmail chat, if the camera icon is green, it means that they are available to chat and have a camera attached. If it is just a green dot, it means they are not available.
The red dot beside the chat is the availability. It shows various types of moods of user. The red dot shows that the user is busy.
The green dot next to the name is the status. It means if a person is available, busy, invisible etc. Green dot means available to chat and message.
if the person in the Gmail chat box has a camera besides their name, that means that the computer they are using has a web cam that is ready to use. this lets the other people know that the person with the camera icon is able to video chat.
One person will log onto their Gmail account and click on the sidebar where there will be people lit up with a green dot next to them. That is where the person will click on them and talk!
That they are in your clan/friends chat.
I don't think there is a way to tell the difference. When I know someone is invisible it looks the same as someone being logged off, it says (name) is unavalible to chat... and instead of the little dot being green it is the grey X. Hope that answers your question!
On the left, below the inbox/spam menu, you can see a chat box, there you have to invite your friends to chat with them. After they accept, you get their name in your chat box. Click their name in the chat box. If they are online, you can chat with them even if they are offline your messages will be sent to them and they can see it when they log on.
ContactLDShadowLady@gmail(dot)com
ContactLDShadowLady@gmail(dot)com
The Gmail green dot is the sign of availability. It shows that the person is available. It can be activated via the hangouts application.