This occurrance is called perigee, when the moon is actually a bit over 31,000 miles closer to the Earth than at any other time of the twenty-nine and a half days of it's orbit. The reason for this is that the orbit of the moon isn't an actual circle but an eliptical shape. The opposite of perigee is apogee - when the moon is the farthest from the Earth.
When the perigee occurs during a full moon such as the one tonight, the moon appears to be just under 15% larger than during the rest of the year. It will also be approximately 30% brighter tonight as well. While perigee happens every month, it will only happen once or possibly twice a year during a full moon. Great photo ops to be had for those with clear skies...
The name Wolf Moon was given to the first full moon of the year by Native Americans in the North-Eastern parts of the United States. Because the hungry wolves howled about the tribes' villages in cold, wet January the name Wolf Moon stuck. They had various other names for the full moons during the rest of the year.
Hope you get a chance to gaze at the moon tonight, wherever you are.