A supermoon is the effect of the lunar orbit carrying the moon into unusually close proximity to the Earth.
What is fascinating is that another "supermoon" will occur next month, on September 28th. This second supermoon, because its proximity will be closer to the Earth than the one we observe tonight, will appear even larger and more brilliant.
People interested in divining the "signs of the times" might find this article, "Blue Moon ahead of rare Blood tetrad means world WILL end in September, warn Christians" of interest.