What is the green dot on snapchat?

The green dot on Snapchat indicates that a friend is currently active on the app and available to chat. It appears next to their name in the chat list. Tapping on their name while the green dot is present will likely open a chat window where you can immediately start communicating. It doesn't necessarily mean they're looking at your profile, but rather just generally using the app. Seeing a green dot is a good sign that you'll receive a quicker response from that particular friend. However, presence of this dot depends on a variety of factors. To understand more about these factors, you can read about Snapchat's Active Status.