I thought it meant the level of surveillance you will be under. Most visas dont have any stars so the visa holder is not under surveillance.
One star means, they track your emails, phonecalls, and addresses. This was done in lieu of the Patriot Act by the Department of Homeland Security in 2003 to ensure they could pre-emtively deter criminal activity arising from foreign passport holders.
Two star means that in addition to logging your emails, phone calls and addresses, they also monitor your net activity in detail, paying particular attention to your browsing habits, like which site you visit on a regular basis (even the ones under Incognito/Private browsing mode), and also monitor your bank accounts to verify where you are getting your funds from and how you are spending them.
I know all this because I met a Peruvian guy and he showed me his passport which had 3 stars. You're lucky you dont have three, because that guy had to live 5 years with a geo-tagged ankle bracelet.
After your visa expires, then you need to request them to remove your stars and they will reissue you another five years without the stars.
Cheers, and try not to let this information worry you.
