What data is the Organic Traffic chart pulling?

The traffic numbers reported in the Organic Traffic chart shown in Site Explorer is a moving average for monthly visits:

Here you can see your monthly organic traffic on any particular date. 

Further Reading

• How accurate is Ahrefs' Organic Traffic metric and how do we calculate it?
• Is Organic Traffic a monthly figure (based on past 30 days)?
• Why does organic traffic exist on the graph for my website when it is not in existence before Dec 2016?