its a movie that came out in the cinemas, Its about giant aliens who came out of a worm hole at the bottom of the sea and they are trying to destroy the planet (they are called Kaijus) so the people built giant robots to fight them (called Jaegers) the robots are piloted by a pair of humans to fight the Kaijus.
From Wikipedia: The Pacific Rim refers to lands around the edges of the Pacific Ocean.
The Pacific Rim roughly overlaps with the geologic Pacific Ring of Fire.
( The Ring of Fire is an area where a large number of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean. In a 40,000 km (25,000 mi) horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements. The Ring of Fire has 452 volcanoes and is home to over 75% of the world's active and dormant volcanoes. It is sometimes called the circum-Pacific belt or the circum-Pacific seismic belt. )
And the movie was not based upon a book. It is an original idea.