Summonings are beasts from another dimension that were given their name because they were able to be summoned from that dimension with magic.
Thousands of years ago, a group of sorcerers discovered a link to another dimension capable of bringing summoned spirits into the world. At first, it seemed like a breakthrough discovery, as mages summoned beings to aid them in battle. Soon, though, disaster struck. The summonings wreaked havoc on the earth, destroying everything in their wake as they went out of control. A group of brave sorcerers gave their blood to seal the portal for eternity in hopes that no summoned being would return to the earth again.
As long as descendants of the sorcerers in the blood pact are loyal and exist in the world, the portal will remain sealed.
There is a special group of summonings called summoners. They are highly intellectual, and they think like humans, with motives and personalities. These summoners control the in and out flow of summonings between the two dimensions. Traditionally, summoners would form pacts with certain humans in the human world and teach them how to control summoing portals.