The alternative online alphabet also known as 1337 is leet, short for leetspeak.
Leet is an alternative spelling system that replaces letters with numerals or symbols resembling them: 3 can stand for E, 1 for L or I, and 7 for T. Thus “leet” can be written as “1337.” It is better described as an orthography or slang style than as a fully separate language, because its rules vary between communities and users.
The word comes from “elite,” reflecting early hacker and gamer usage in which being “leet” suggested unusual skill or status. Leet became associated with bulletin boards, online games, hacker culture, and later internet memes. Forms such as “n00b” for “noob” and “h4x0r” for “hacker” are recognizable examples.
Leet is sometimes confused with SMS shorthand, but the systems have different origins. SMS shorthand abbreviates words to save space or typing, whereas leet primarily alters spelling through visual substitutions, sometimes to express identity or evade simple filters.