Google is your friend! It started out as an offshoot of the Michelin Guides. It's a fairly selective rating of restaurants from 1 to 3 stars. It is purportedly very snootily French in character, leading to all sorts of controversies.
One star: A good place to stop on your journey, indicating a very good restaurant in its category, offering cuisine prepared to a consistently high standard.
Two stars: A restaurant worth a detour, indicating excellent cuisine and skillfully and carefully crafted dishes of outstanding quality.
Three stars: A restaurant worth a special journey, indicating exceptional cuisine where diners eat extremely well, often superbly. Distinctive dishes are precisely executed, using superlative ingredients.
Be prepared to pay up for increasing numbers of stars.
Bon Appétit!