The American Standard Code for Information Interchange, which everyone calls ASCII, is a character set which a computer uses to store characters. ASCII specifies a method for computers to store printable characters such as letters A to Z, a to z, digits 0 to 9, punctuation, and spaces. ASCII also includes control characters such as newline. Most computers either use ASCII, or a superset of ASCII that adds more characters, such as accented letters, Cyrillic letters, CJK characters, or hieroglyphics.
NetHack uses ASCII for everything. The source code is in ASCII. If you play in tty mode, everything on the screen is ASCII. Also, ASCII corresponds nicely with the keys found on most QWERTY keyboards in the United States. In fact, in modern NetHack 3.x.x, the dungeon contains every printable ASCII character except "6", "7", "8", "9", and "," (the comma). Some older versions of NetHack did use "8" for Medusa and "9" for giants, but NetHack 3.0.0 made monster symbols refer to classes of monsters rather than necessarily single monsters, and now Medusa is @ and giants are H.
The printable ASCII characters are:
The characters in the above tables all link to their informational page. The goal is to create an article in Wikihack for every character. In the article, mention which monster or object that character represents, and what that key does from the keyboard. Try to link to other articles; for example, d should link to both dog and drop.
NetHack also uses some non-printable ASCII characters for commands. Those are commands that use Ctrl key. Pressing Ctrl and another character sends a non-printable character. Alt key has similar function.
For technical reasons, angle brackets, curly brackets, square brackets, hash marks, pipes, or plus signs can not be used in the names of articles. Also, an article name cannot contain only underscores, and it cannot consist of exactly one or two dots. Thus all of those articles have words for names.