Magic Formula

Ars Magus (術式, Jutsushiki, Skill Formula) is the use of science to manipulate Seithr. The knowledge for how to perform each ars is recorded in a Grimoire.

Information
During the Dark War, Nine of the Six Heroes passed her Magic to mankind but humans were unable to use Magic in its basest form as they were not capable of handling or manipulating it. Therefore, in order to make use of it, humanity did a great deal of research into the subject and eventually developed what is now known as "Ars Magus". By using science to manipulate Seithr that came from the Black Beast, ars magus could be used to many ends. In order to use ars magus, one would have to recite the ars, or "spell". When ars magus was first developed, the creators found that the power and effectiveness of a grimoire varied with its user. Since that discovery, mankind was able to produce more efficient ars magus. Unfortunately, Ars Magus alone was not enough to defeat the Black Beast and mankind knew they would need more power and developed Ars Armagus, or "Armagus".

Japanese Wikipedia Translation
(The following is an approximate translation of the citation of Wikipedia in Japanese.)

術式

Ars Magus (Skill Formula) 「魔法」と「科学」を融合させ、人類にも魔法の断片を扱うことを可能にした技術. The technique, [formed] through combining 'Magic' and 'Science', to make humans possible of handling fragments of magic. 魔道書に記された「コード」を読み上げることにより、大気中の魔素を消費して行使する. 術式の使用には適正があり、高ければ高いほど数少ない魔素消費で術式を扱うことが可能になる. しかし適性が低いと燃費が悪くなり、最悪、術式自体を使えないほど適性が低いということもある. By reciting the "code (Ars) " stated in a grimoire, [Ars Magus can be] performed through the consumption of Sethir within the atmosphere. There is compatibility for the use of Ars Magus, the higher the compatibility number(rate) the less Seithr that can be consumed possible. But [with]low compatibility and low consumption, worse [case,]the Ars Magus itself cannot be used by the low compatibility [user] sometimes. また、「書」とはいっても本の形をしているわけではなく、その使用方法からそう名付けられているだけに過ぎない. 魔道書は現在統制機構の管理下にあり、不許可に所持することは違法である. Also, the "Grimoire" mentioned may not necessarily be in the form of a book, [it] is just merely named so by the way to use it. The grimoires are currently under the control of the N.O.L., that unauthorized possession [of them] are illegal.