Notarikon

Notarikon (ノタリコン) is a method of deriving a word, akin to the creation of an acronym, by using each of inital or final letters to stand for another word, forming a sentence or idea out of the words. The word "notarikon" is borrowed from Greek language (νοταρικόν)), which in its turn was derived from the Latin word "notarius," meaning "shorthand writer."

In Toaru Majutsu no Index it is referred to as a quick Kabbalah reading method. It is a unique pronunciation method of only using the first alphabet, with the aim of turning it into a code and making it quicker to read.

In relation to the story
The technique is used in Toaru Majutsu no Index specifically that of Index's Spell Intercept. Kazuma Kamachi's technique is to have a sentence he had writtend translated into English first and then using the first letters of each word for the "codes" used for her Spell Intercept. Below is the code used by Index for her Spell Intercept of Sherry Cromwell's golem, as shown in the original Japanese light novel : "M B F P A D C O G"

The accompanying meaning for it in the original Japanese text, as well as the romaji:

"「両足を平行に配置し重心を崩せ」" ("Ryōashi o Heikō ni Haichi Shi Jūshin o Kuzuse")

And the literal meaning of the above sentence:

"Place both legs parallel and destroy the center of gravity." One can then conjecture the translated meaning of the codes used:

"Move Both Feet Parallel And Destroy Center of Gravity"

Other users
Stiyl Magnus uses the notation to quickly disperse bystanders with a spell, during the scene where he and Kamijou Touma discover the bloodied body of Himegami Aisa after Oriana Thomson attacked her.