What is what does it mean when there is a green dot on snapchat?

The green dot on Snapchat indicates that a friend is currently active on the app and is likely available to chat. It appears next to their display name in your chat list. It doesn't necessarily mean they're looking at your chat, just that they are using the app. The green dot appears for friends that have Active Status turned on. If you or your friend have disabled Active Status, you won't see the green dot, even if you are both actively using Snapchat. So, absence of the green dot does not mean they aren't using the app, only that their active status isn't visible.